BOSTON -- There was a stretch of games during the regular season in which Boston Celtics point guard Isaiah Thomas so routinely produced spectacular performances that coach Brad Stevens said it was no longer possible for him to be amazed by anything Thomas did.

Stevens would be the first to admit now that he was wrong.

Because what Thomas has done the past two weeks is so far beyond comprehension, it has left Stevens and Thomas' teammates unable to find the words to properly describe what they are witnessing. Al Horford went with "unbelievable"; Stevens has suggested "unfathomable" and "unreal." None of those seem strong enough to properly describe the way Thomas has persevered in the face of impossible grief after the death of his younger sister.

When Thomas found the strength to play in the immediate aftermath of his sister's passing, it seemed inconceivable. When Thomas rallied his team from an 0-2 deficit against the Chicago Bulls despite his obvious grief, it felt unimaginable.

When Thomas made a cross-country dash back to Boston after trekking to Tacoma, Washington, for his sister's funeral on Saturday and then, short on sleep, scored 33 points in Boston's Game 1 win over the Washington Wizards on Sunday, it seemed incomprehensible.

But then there was Tuesday. What would have been his sister Chyna's 23rd birthday. A day that Thomas spent much of at a local hospital while undergoing a second round of oral surgery to repair the damage inflicted when one of his front teeth was dislodged in that Game 1 victory.

Thomas understandably struggled to find energy in the hours before tipoff, and Horford admitted, "A lot of guys wouldn't have even played this game."

But Thomas did not believe that was an option. Not after the stirring words he had offered as part of his sister's eulogy three days earlier. In saying goodbye to his sister, Thomas noted how, for the first time in his life, he felt like quitting when he first learned the news of her passing following a single-vehicle accident on April 15.

Instead, he pledged to keep going in her memory.

So on Chyna Thomas' 23rd birthday, Isaiah Thomas scored 53 points to will his team to a 129-119 triumph over the Wizards at TD Garden. On a night when he required a personalized mouthguard to protect his surgically repaired teeth, Thomas fearlessly attacked the basket while scoring 29 points in the fourth quarter and overtime. He simply refused to let this game get away.

It's a journalist's job to find the proper words to put situations like these in perspective. But like Thomas' coach and teammates, we're admittedly struggling here. It would seem fair to suggest that Thomas can't possibly do anything more remarkable than what we saw Tuesday.

And yet Stevens probably wouldn't be willing to say that again. Because Isaiah Thomas continues to amaze.

"What else is there to say?" Stevens said after Tuesday's win. "There's a point today when he was not feeling good at all and was having a tough day. And I thought he was going to really have to gut this one out. And he not only guts it out, he ends up with 50. Pretty impressive."

During an on-court interview with TNT following the game, Thomas fought back emotions while detailing how this was his sister's birthday and how she served as his inspiration.

"My sister wouldn't want me to stop," Thomas said, his voice wobbly. "The only thing about it is, once I leave this gym, I hit reality and she's not here. So that's the tough part. But, when I'm in this arena, I can lock in and I know everything I do is for her."

Ignore all else going on around Thomas and his performance was remarkable on its own:

• His 53 points were the second-highest postseason output by a Celtics player, trailing only John Havlicek's 54 in 1973.

• He became the first Boston player to record a 50-point game in both the regular season and playoffs.

• His 29 points in the fourth quarter and overtime were just one point fewer than the Wizards scored as a team in the same span.

• He has scored 86 points in the first two games of this series. That's the highest combined total ever in the first two games of a series, according to Elias Sports Bureau.

"It's been a lot of fun just watching him work, perform, just making the right plays," Horford said. "It's hard in the heat of the moment to know when to pass, when you got it going like that, or when to score. Isaiah seems so poised every time. Making the right decision, when to pass the ball, when to shoot it, and you can't be mad at him because he's scoring the ball so well when he's taking shots, he just has that feel.

"Not a lot of people have that feel to do both, and he's able to do it. Honestly, I didn't even know he had that many points. I all of a sudden looked up and saw 51. He's just steady, steady, steady, and just the credit goes to him. After going through all that he's been going through with the tooth and everything, I just don't think a lot of guys would have even played this game. It's something special after what he's gone through the past 24, 36 hours to come out and drop 53."

In typical Thomas fashion, he's already dreaming bigger.

"It's nice for your name to be in Celtics history because of all the great players, but until you win one of those championships you can't call yourself a great player," he said. "That's the ultimate goal."

Thomas admitted he has dreamed about playing his best basketball on the NBA's biggest stage. He entered the season with a desire to learn how to win in the postseason and, with six straight playoff victories, he has positioned the Celtics to make the leap to the Eastern Conference finals.

One of my new year's resolutions was to not be surprised anymore by anything Isaiah Thomas does. So, 51 points? Not surprised.

— J.A. Adande (@jadande) May 3, 2017

There is still work to be done in this series. But Thomas has plenty of motivation. He noted how legends are born in the postseason.

What Thomas might not realize in the moment is that he might have already etched his place in Celtics lore. What he did Tuesday night and what he has done this entire postseason defies words.

But one thing is certain: Thomas continues to amaze.