OAKLAND, Calif. -- A memorable 18-0 third-quarter run sparked by Golden State Warriors guard Stephen Curry -- combined with the loss of San Antonio Spurs forward Kawhi Leonard, who re-aggravated his left ankle injury -- produced a historic 113-111 comeback victory in Game 1 of the Western Conference finals.

The Warriors trailed by as many as 25 points and faced a 20-point deficit at the half on Sunday. According to ESPN Stats & Information research, it’s the largest comeback win in a conference finals game since 2002, when the Boston Celtics came back from 26 down to beat the New Jersey Nets in Game 3. And it’s tied for the third-largest halftime comeback in NBA postseason history.

“It was actually a perfect Game 1,” said Warriors forward Draymond Green, who finished with nine points, seven rebounds and seven assists. “You get punched in the mouth, but yet you can still get the win."

Curry recorded a game-high 40 points on 14-for-26 shooting and 7-of-16 from beyond the arc. Kevin Durant supplied 34 points and five rebounds.

But before Leonard's exit, Golden State had dug itself quite the hole.

Some early carelessness led to six first-quarter turnovers for the Warriors, and after coasting to two straight sweeps to open the postseason, Golden State had suddenly suffered its ugliest opening quarter of the playoffs.

Spurs forward Jonathon Simmons drained a 3-pointer to put his team up 12 late in the first. Curry sprinted up the floor and launched a questionable 32-footer that found nothing but air with 28 seconds left. Another Warriors turnover soon followed, resulting in a two-on-one transition advantage in which LaMarcus Aldridge finished with a dunk right before the first-quarter buzzer sounded.

The Spurs were up 30-16 and extended it to 25 midway in the second quarter.

“I think we were a little bit too relaxed,” Durant said. “Instead of taking the game, we let it come to us a little bit. I think that’s good sometimes, but against a team in the Western Conference finals, you just got to go.”

A stunned Oracle Arena watched as the Warriors tried to fight their way out.

After Curry knocked down a pair of free throws in the second, he stole the inbounds pass and swished a right-corner 3. For the first time all game, the crowd erupted as the Warriors capped an 11-0 run with 5 minutes, 5 seconds left to play in the half. Golden State was down 14.

However, a 16-10 Spurs run to close out the half gave the visiting team a 20-point lead at intermission. Leonard and Aldridge combined for 35 points in the first half, seven points fewer than the entire Warriors' score.

Warriors coach Steve Kerr, who is out indefinitely as he finds a cure for his migraines and nausea stemming from back surgery almost two years ago, addressed the team at halftime with a passionate speech on playing their game.

“It’s always great to hear Coach Kerr’s voice and give his perspective,” Curry said. “It’s actually a fresh perspective from somebody who is watching the game, so he sees a lot of different angles and he sees how things are developing from a broader perspective. So, that’s obviously huge for us.”

The Warriors’ largest comeback win on the season was from 22 down against the Spurs on the road on March 29. According to ESPN's In-Game Win Probability, the Warriors had an 11 percent chance of coming back and winning this game.

But the odds would not be in the Spurs’ favor Sunday afternoon.

Early in the third, Leonard, who is already playing on a tender left ankle, slipped along the sideline after knocking down a 3-pointer, and immediately came up hobbling down the court. Grimacing in pain, he signaled to come out. He did return shortly after but experienced another setback when Golden State big man Zaza Pachulia landed on his left foot while he attempted a long 2-pointer.

Pachulia was whistled for the foul. Leonard could barely move. The two-time NBA Defensive Player of the Year made his two free throws and then exited to the locker room limping severely. He was unable to return.

Some fans and media charged Pachulia for intentionally trying to injure the small forward. Leonard didn’t see it like that.

“Did he step under it? Like on purpose? No, he was contesting the shot, the shot clock was coming down,” Leonard said. “I’ll have to see the play.”

Durant also weighed in.

“Zaza’s not a dirty player. You’ve got to time that perfectly if you want to hurt somebody. I mean, we’re not that type of team. … You can’t listen to people on Twitter. They’re irrational, so I don’t know.”

The Spurs had a 78-55 lead with 7:53 left in the third quarter once Leonard subbed out for the final time. The Warriors smelled blood.

With Leonard out, the back-to-back defending conference champs commenced an electrifying 18-0 run that lasted a little less than four minutes.

Curry poured it on in the quarter, scoring 19 points on 7-of-10 from the field, including 4-of-6 from deep, to go with four boards and three assists. Those 19 points accounted for his highest scoring quarter in any game over the past two postseasons.

Golden State had rallied back to within five with 4:26 remaining in the quarter, setting up the stage to take the game in the fourth.

Golden State scored 42 points in the first half, but then 39 in the third quarter. The Warriors held the Spurs to 21 points in the final 12 minutes; they scored 32.

All Leonard could do was watch it all unravel from the locker room.

“I saw [our lead] at eight when I turned on the game but, yeah, it was pretty tough,” he said. “But I still have faith in them.”

Spurs coach Gregg Popovich was asked if his team got rattled after Leonard departed.

“You think so?” he responded back. “Did you notice that?”

Aldridge ended the game with 28 points and eight boards, but five of his six turnovers came after Leonard left the game for good. Leonard put in 26 points and eight rebounds in just under 24 minutes.

Warriors super reserve Andre Iguodala played only 10 minutes. He has been bothered by left knee soreness. A team source told ESPN that Iguodala was limited in scrimmages leading up to this game. He will undergo an MRI on his left knee Monday, a league source told ESPN.

It was a sigh of relief vibe in the Warriors’ locker room after the contest. Collectively, they were disappointed in the start, but ecstatic with the finish.

“It was definitely a nice way to win Game 1,” Curry said. “We’ve got to capitalize off that and start Game 2 a lot better.”

Game 2 is Tuesday.