Luka Doncic wasn't about to let a sprained ankle slow him down, nailing a game-winning three-pointer at the buzzer to lift the Dallas Mavericks to a 135-133 overtime playoff win over the Los Angeles Clippers on Sunday.

The 21-year old Slovenian phenom, who was playing with a tender ankle and missing his offensive sidekick Kristaps Porzingis, finished with 43 points, 17 rebounds and 13 assists to level the first-round NBA Western Conference playoff series at two games each.

"This game was from another planet," said Mavericks coach Rick Carlisle of Doncic's heroics.

Luka Doncic of the Dallas Mavericks is mobbed by teammates as they celebrate his game-winning three-point basket against the LA Clippers at the buzzer in overtime
Luka Doncic of the Dallas Mavericks is mobbed by teammates as they celebrate his game-winning three-point basket against the LA Clippers at the buzzer in overtime GETTY IMAGES NORTH AMERICA / Kevin C. Cox

Doncic made a basket with 50 seconds left to tie the score 130-130 then gave Dallas a two-point lead with a spinning move to the basket with 19 seconds remaining.

He capped his triple-double with a 27-foot step-back jumper from the left side as time ticked down, sparking a wild celebration on the floor in the NBA's quarantine bubble in Orlando, Florida.

"I can't explain the emotions I had when I saw the ball go in," Doncic said. "When I saw the whole team coming towards me that was one of the best feelings I have ever had as a player."

While Dallas levelled their series, Boston became the first team to reach the second round with a 110-106 victory over the Philadelphia 76ers.

Coach Brett Brown and medical staff tend to Philadephia forward Tobias Harris after his hard fall in the 76ers NBA playoff loss to the Boston Celtics
Coach Brett Brown and medical staff tend to Philadephia forward Tobias Harris after his hard fall in the 76ers NBA playoff loss to the Boston Celtics GETTY IMAGES NORTH AMERICA / POOL

Kemba Walker scored 32 points and Jayson Tatum added 28 and 15 rebounds for the Celtics, who swept the Eastern Conference first-round series 4-0.

Kemba Walker of the Boston Celtics shoots against Joel Embiid of the Philadelphia 76ers during the first quarter in Game Four
Kemba Walker of the Boston Celtics shoots against Joel Embiid of the Philadelphia 76ers during the first quarter in Game Four GETTY IMAGES NORTH AMERICA / POOL

Doncic, who is playing in his first NBA playoffs, carried the Mavericks Sunday without Porzingis, who was a late scratch because of a knee injury.

But the pre-game buzz was all about Doncic's health, not Porzingis. Doncic sprained his left ankle in the second half of game three and had an MRI on Saturday to determine the extent of the damage.

"This morning I wasn't feeling good but as soon as I stepped on the court I knew I could go," said Doncic, who recorded his second straight triple-double.

Said Carlisle: "He sees the game in 6G, not 5G. He is a very special player."

Donovan Mitchell of the Utah Jazz joined Michael Jordan and Allen Iverson as players with multiple 50-point games in a playoff series
Donovan Mitchell of the Utah Jazz joined Michael Jordan and Allen Iverson as players with multiple 50-point games in a playoff series GETTY IMAGES NORTH AMERICA / Kevin C. Cox

Trey Burke added 25 points, Tim Hardaway scored 21 and Seth Curry chipped in 15 points for Dallas, who led by 12 with nine minutes remaining in the fourth quarter.

Lou Williams had 36 points and Kawhi Leonard finished with 32 points for the Clippers, who blew a 21-point first-half lead.

Game five is on Tuesday.

Dallas Mavericks star Luka Doncic shoots over Reggie Jackson to hit the game-winning three pointer against the Los Angeles Clippers during overtime in game four of the Western Conference first round playoff series in the NBA quarantine playoff bubble
Dallas Mavericks star Luka Doncic shoots over Reggie Jackson to hit the game-winning three pointer against the Los Angeles Clippers during overtime in game four of the Western Conference first round playoff series in the NBA quarantine playoff bubble GETTY IMAGES NORTH AMERICA / Kevin C. Cox

Meanwhile, the Celtics' Walker, who arrived in Boston after eight seasons of frustration with the Charlotte Hornets, was basking in his first NBA playoff series win.

"It feels good," Walker said but added: "The work's not done. We won a series, but we're still looking forward to some more tough ones."

With their backs against the wall, Joel Embiid and the 76ers kept it close and trailed by just two points late in the third quarter before forward Tobias Harris took a hard fall under the basket, his head slamming the hardwood.

Harris was able to leave the court under his own steam, holding a towel to his left eye and temple, and returned after treatment for what the team said was a cut over the eye.

But the Celtics closed the third quarter on a 12-0 run that effectively ended the 76ers' hopes.

"I feel like the game flipped when Tobias went out," Sixers coach Brett Brown said.

The Celtics will face the defending NBA champion Toronto Raptors who moved onto the next round after sweeping the Brooklyn Nets.

Reserve Norman Powell scored a career playoff high 29 points and the Raptors won their series with a dominating 150-122 victory in Orlando.

Serge Ibaka came off the bench to score a playoff career high 27 points and grabbed 15 rebounds for Toronto, who swept a best-of-seven series for the first time in their franchise history.

The Raptors, who set a franchise record for points in a playoff game with 150, will play the Boston Celtics in the Eastern Conference semi-finals, beginning Thursday.

Toronto played most of Sunday's contest without guard Kyle Lowry. Late in the first quarter, Lowry headed to the dressing room after twisting his ankle. He did not return.

In the late game, Donovan Mitchell delivered a 50-point performance for the second time in the series as the Utah Jazz edged the Denver Nuggets 129-127 to grab a 3-1 series lead.

Mitchell finished with 51 points, including four three-pointers, as the Jazz had to withstand a 50-point night from Canadian Jamal Murray of the Nuggets.

Mitchell, who scored 57 points in game one, joined Michael Jordan and Allen Iverson as players with multiple 50-point games in a playoff series.