LAKE BUENA VISTA, Fla. >> Facing the absolute brink, the Toronto Raptors suddenly have life.

OG Anunoby caught a crosscourt inbounds pass from Kyle Lowry and hit a 3-pointer with no time remaining, and the Raptors beat the Boston Celtics 104-103 in Game 3 of the Eastern Conference semifinal series tonight.

Toronto cut Boston’s series lead to 2-1. The Celtics took a two-point lead when Kemba Walker found Daniel Theis for a dunk with a half-second left.

No team in NBA history has rallied from a 3-0 series deficit. The Raptors won’t have to try it now; Lowry elected to audible and throw the long pass — high over 7-foot-5 Tacko Fall — to Anunoby.

Lowry played virtually the whole way, finishing with 31 points, eight assists and six rebounds. Fred VanVleet scored 25 points, Pascal Siakam had 16 and Anunoby 12.

Walker scored 29 points for Boston, which lost for the first time in seven playoff games. Jaylen Brown had 19 points and 12 rebounds and Jayson Tatum finished with 15 points, nine rebounds and six assists for the Celtics.

Marc Gasol made a layup with 5:57 left for a four-point lead; the Celtics responded with the next eight points, going up 99-95 on a dunk by Brown with 3:02 remaining.

Lowry got a pair of layups, both drawing Toronto within two. The Raptors had the ball with a chance to tie or take the lead in the final half-minute, VanVleet getting an acrobatic layup to drop with 21.5 seconds left and knotting it at 101.

Theis’ score left Toronto needing a miracle. Anunoby delivered.

“I had confidence in him,” Lowry said. “We’ll take that win.”

Siakam was called for his third foul on a charge with 7:44 left in the half; Raptors coach Nick Nurse used his lone challenge to protest, but replay upheld the call — a big decision against Toronto.

When Siakam took a seat for the rest of the half, Toronto trailed 38-37. The outlook got very bleak very fast without him on the floor.

The Raptors got outscored 19-10 over the 6:42 that followed going into the break, and the Celtics stretched the lead to 57-47 by the half. Walker had 17 points in the first quarter, capping that period with a 3-pointer — and did it again to end the second to give Boston what was then its biggest lead.

Lowry had been 0 for 5 from 3-point range in the game — and 1 for 17 in the series — before connecting from the left corner midway through the third, getting the Raptors to 61-60. Toronto would eventually lead by as many as four in the third, but Boston reclaimed the lead and took an 80-76 edge into the fourth.

TIP-INS

>> Raptors: Lowry sat for a 1:31 stretch of the first quarter. He returned late in that period and played the final 37 minutes, 29 seconds. … Nurse tied Dwane Casey for the franchise postseason wins lead, with 21.

>> Celtics: Walker’s 17 first-quarter points were a career-best for any postseason quarter. He had 14 for Charlotte in the fourth quarter against Miami on April 29, 2016. … Robert Williams’s first shot attempt of the night was blocked by Serge Ibaka with 8:19 left in the first half, significant because Williams had been 10 for 10 in the series to that point.

RARE OPPORTUNITY

It’s rare for a third-seeded team to sweep a second-seeded team in a best-of-seven — and it won’t happen in this series now. There’s been only two such instances in NBA history —Dallas over the Los Angeles Lakers in the 2011 West semifinals and Philadelphia topping Milwaukee in the 1985 East semifinals.

NURSE ON NASH

Nurse is friends with new Brooklyn Nets coach Steve Nash and had talked to him quite a bit of late — but Nash didn’t reveal that he was in the mix for the job. “Caught me off guard, that’s for sure,” Nurse said. “He kept all that to himself, close to his chest. … He’ll be great, man. He’s one of the greatest players ever.” Nash’s hiring was announced Thursday morning. He’s the second Canadian to become an NBA head coach, joining Jay Triano.

UP NEXT

Game 4 is Saturday.