LOS ANGELES — Of all the players on the court Monday, it wasn’t LeBron James who won it. Or Anthony Davis. Or Stephen Curry or Klay Thompson.

It was Lonnie Walker IV.

Yes, Lonnie Walker IV.

The Lakers’ reserve guard scored all 15 of his points in the fourth quarter to lift the Lakers to a 104-101 victory and an imposing 3-1 series lead over the Golden State Warriors in the Western Conference semifinals.

Walker IV didn’t attempt a shot until the fourth quarter, when he made six of nine to help the Lakers eat away at a seven-point deficit in front of a delirious crowd at Crypto.com Arena.

He was a forgotten man in the Lakers’ rotation the last six weeks, drawing the dreaded DNP-Coach’s Decision in 12 games and playing limited minutes when he did appear in a game.

Safe to say he wasn’t forgotten Monday.

When it was over, and Walker IV carved out a piece of Lakers’ playoff lore for himself, he called his effort “the greatest feeling you can ever, ever imagine.”

LeBron James and Anthony Davis embraced him immediately after the game, which ended with two uncharacteristic turnovers by the Warriors down the stretch, one by Draymond Green and one by Curry.

Curry tried his best to knot the series at two games each but missed a turnaround jumper with 26.4 seconds left and, after Green corralled the offensive rebound, misfired on a 29-foot three-point shot. Curry had a triple-double — 31 points, 14 assists and 10 rebounds — but made only three of 14 three-point shots.

With the Lakers desperately trying to win at home, Walker IV started his personal fourth-quarter run by drilling a three-pointer. Then he won a footrace to a loose ball off a Golden State turnover, turning it into an easy two at the other end.

Then came a baseline jumper. And a jumper up top as the shot clock wound down. Then a floater in the lane, followed by a shot over Curry and, finally, a pair of free throws.

Walker IV, only 24 years old, became the first Lakers reserve with 15 points in the fourth quarter since Kobe Bryant in 1997.

“We don’t win this game without Lonnie Walker tonight. That’s for sure,” James told TNT.

Walker IV started the first 32 games he played for the Lakers after signing a one-year contract as a free agent last July. After his solid start, he was injured and missed almost a month because of tendonitis on his knee.

Shortly after he returned, the Lakers executed a flurry of trades that brought six new players to the team. Walker IV quickly found himself on the outside looking in, a former starter relegated to the end of the bench.

“There’s a lot of uncontrollable things you can’t control,” Walker IV said. “I stuck with it. Stayed in the gym, still being a great teammate.”

James, for his part, had 27 points, nine rebounds and six assists. He knew how important it was to win this game, in case his whopping 43 minutes didn’t show it.

“We’re just a resilient bunch. They hit us with haymaker after haymaker after haymaker, trying to get us to fall,” James said. “We stayed in there for 12 rounds and was able to hold on.”

Game 5 is Wednesday at Golden State. If the Lakers win, they’re on to the West finals against Denver or Phoenix.

Davis predicted the aura at Chase Center would be filled with “urgency, desperation.”

“We know what the environment will be in their arena,” Davis said. “We’ve gotta make sure we come out with the right mindset.”

Davis broke up a curious streak in this year’s postseason that saw him dominate odd-numbered games in playoff series but struggle in even-numbered ones.

He had 23 points and 15 rebounds while also playing 43 minutes in Game 4.

Austin Reaves broke out of a mini-slump, scoring 21 points Monday after shooting only 32% in the first three games of the series.

But Walker IV had the numbers that mattered in crunch time. Thanks to him, the Lakers are a win away from disposing of the defending champions.