There are momentum swings in an NHL postseason series. And then there’s what’s happening between the Edmonton Oilers and Vegas Golden Knights.

The Golden Knights lead the Oilers 2-1 in their Western Conference second-round series after a decisive 5-1 victory in Game 3 on Monday. That came after Edmonton walloped Vegas by a 5-1 score in Game 2. And that followed a wild Game 1 where the Golden Knights blew one (and nearly another) multi-goal lead but hung onto a 6-4 win.

All that is to say, it’s tough to know exactly what to expect from these powerhouses in Game 4 (10 p.m. ET, ESPN). Will the offensive pendulum continue to swing, with another trip back Edmonton’s way? Or does defense (and discipline) win the day in a tight-checking, low-scoring sort of way that hasn’t materialized in the series to date?

More importantly, who comes out on top before the sides shift back down to the desert?

Here we have the X factors for Game 4 — from players, to stats, to a key element that could spell victory, or contribute to defeat — for either team in this next pivotal matchup.

X factor: Key player

Edmonton: Stuart Skinner

Goaltending is imperative to playoff success. Obviously.

In this instance, all eyes will be on Skinner to see how he bounces back, and potentially puts a stop to the five-plus goal games defining this series.

The Oilers rookie was pulled from Game 3 after allowing four goals on 23 shots. Skinner was also sub-par in Game 1’s defeat, giving up five goals on 33 shots.

For as much as Edmonton has been on a roller coaster during this series, so too has Skinner, enduring notable ups and downs throughout the postseason. In Oilers’ victories, Stuart owns a .921 save percentage and 2.51 goals-against average. In losses, he’s got an .857 SV% and 4.67 GAA.

Pitted against the Golden Knights thus far, Skinner is 1-2-0 with an .885 SV% and 3.96 GAA. Those totals suggest there’s more Stuart can give to Edmonton — and he’ll likely have a chance to do that in Game 4. Despite questions surrounding whether Jack Campbell would get the call — he made nine saves on 10 shots in relief on Skinner in Game 3 — it was Skinner back in the starter’s net for Tuesday’s practice. Coach Jay Woodcroft wouldn’t confirm on Tuesday it would be Skinner in net for Game 4, but all signs certainly pointed that way.

Edmonton spent a disproportionate amount of time in Game 2 on the power play — and capitalized with three goals — which took pressure off Skinner to stand on his head as the Oilers evened the series at 1-1. It’s unlikely the Oilers will see that much special teams influence in Game 4. Should he be the Oilers’ starter again on Wednesday, it’ll be on Skinner to showcase his best work (particularly at even strength) and renew confidences in the type of difference-maker he can be moving ahead in this series.

Vegas: William Karlsson

The Golden Knights had a star in William Karlsson throughout their first-round series against the Winnipeg Jets.

Karlsson tied Chandler Stephenson for the team lead in goals (4), had the second-best shooting percentage (36.4%) and was an impressive 55.6% in the faceoff dot.

That output hasn’t carried over — yet. Karlsson grabbed just one assist against the Oilers (from that Game 1 win), has only seven shots on goal in the series and dropped to 51.1% in the dot.

One of the great strengths to Karlsson’s game is he’s a strong two-way player who can contribute at both ends of the ice. Going up against the likes of Connor McDavid and Leon Draisaitl in this series is also different than what Karlsson experienced versus the Jets. What would help Vegas most in Game 4 is some added output from Karlsson on the scoresheet, too. He’s capable of that, making him a key player to watch not only shutting down top skaters but providing an offensive boost as Vegas looks for more depth of scoring.

Karlsson should have ample opportunity to break out of that mini scoring slump. He’s averaging nearly 18 minutes of ice time per game, with a presence on the power play and shorthanded. Versatility like that rarely goes unnoticed — or unrewarded — for long. And after seeing Jonathan Marchessault, Jack Eichel and Stephenson go off in Game 3, Karlsson should definitely be feeling like it’s his time to shine again, too.

X factor: Standout stat

Edmonton: Excellent on the rebound

How good are the Oilers coming off a loss? Extremely.

Edmonton hasn’t dropped consecutive games since February 25-27. All six of their defeats since then — including three in this postseason — have been followed by wins. And in all three of those victories, the Oilers have scored four or more goals.

It’s a pattern with real staying power and shows the resiliency Edmonton could wield to its advantage on home ice Wednesday. In a series that’s seen so much back and forth already, the Oilers won’t hesitate to tap into anything that’s helped them weather adversity before and get back on equal footing with the opposition.

Vegas: Even-strength warriors

Every team has to find its edge. The Golden Knights’ might be their play at even strength.

In this series, Vegas is outscoring Edmonton 10-4 at 5-on-5. Meanwhile, they’re getting outscored 5-1 on the power play.

Therefore, it would be wildly advantageous for Vegas to a) stay out of the penalty box in Game 4, and b) force the Oilers into playing as much as possible at even strength.

The Golden Knights had similar success at 5-on-5 in the first round, not only leading the postseason field in even strength goals, but outscoring the Jets in that category 15-6 (while again being outscored on the power play, 5-3).

Another way to look at this for Vegas might be that their penalty kill has been a postseason letdown (currently the worst among remaining playoff teams, at 56.5%). Whatever way you slice it, Vegas’ best chance of topping the highly skilled, high-flying Oilers is making them earn their offense at 5-on-5. That’s not where Edmonton has excelled so far. Vegas will want to see that carry on into Game 4 and beyond.

X factor: Area of opportunity

Edmonton: More balanced offensive attack

The Oilers have a pair of all-world talents in McDavid and Draisaitl driving their offense — often from the same line.

What Edmonton saw in Game 3 was a need to start spreading the wealth.

Zach Hyman was hobbled by a lower-body collision with Nicolas Hague during the first period of Game 3 that limited his ice time (down from his usual 20 minutes per game to just 14:06) and put a spotlight on how the Oilers’ depth players needed to start making more of an impact on the series.

Edmonton has had four scorers total against Vegas: Draisaitl (6), McDavid (2), Evan Bouchard (1) and Warren Foegele (1). Separating McDavid and Draisaitl — who began playing together again during Edmonton’s first-round series against Los Angeles — could help kickstart some other skaters into gear (namely Evander Kane and Ryan Nugent-Hopkins).

“We spend a lot of time talking about trying to set the conditions that are most favorable for our team,” Woodcroft said on Tuesday of shifting McDavid and Draisaitl to different units. “We move them around the chess board quite often. For us, sometimes if we feel that’s a punch in the arm we need, we might [have them together]. Very rarely are we stuck in one way of thinking. I think that comes from knowing your team personnel and I think our interchanging of parts is what makes us a dangerous team; it’s part of who we are.”

Hyman has been the Oilers’ third-most important forward in the postseason behind the team’s superstars. He did not practice on Tuesday, and if he’s not available for Game 4, it’s even more imperative Edmonton find contributions elsewhere.

Case in point: the Oilers’ third line of Foegele, Ryan McLeod and Derek Ryan. They’ve really appeared to starting jelling — it was Foegele opening the Game 3 scoring off a feed from Ryan — and if Woodcroft can pry some more output from them, it would remove added pressure from the top six.

Regardless of specifically whom that production comes from, Edmonton knows improvements have to be made in their 5-on-5 offensive play. Digging into the team’s depth is their best course of action.

Vegas: More production from the blue line

The Golden Knights’ defense hasn’t realized its full offensive potential.

In three games against Edmonton, Vegas’ back end produced one goal (from Zach Whitecloud in Game 3) and seven total points.

In five games against Winnipeg, the Golden Knights got zero goals and eight points out of its blue line.

What if that were to change?

“We’d like a little bit more [from the defense],” coach Bruce Cassidy said Tuesday. “Got a big goal from Zach the other night. But for this particular series, we have to be real careful how much we’re wandering from the back end and how quick they can come back at us. I think the guys want to make sure you’re in position defensively and not be reckless, but you still in today’s game have to be on the attack and on the move.”

Naturally, the defense’s first job is keeping pucks out of the net. But Vegas’ lack of offensive production from that area is worth exploring — and ideally tapping into.

Playoffs are all about evolution. How can a team improve on the fly without having to make drastic changes? This is an easy area of adjustment for Vegas that could pay major dividends right away. Whether it’s blasting shots from the point through traffic, supporting forwards on the cycle or just getting pucks on net for rebound tries, seeing the Golden Knights’ defense become more engaged and in tune with its offense would add another element to their arsenal that the Oilers would have to account for moving ahead.

And what team wouldn’t want that?