Thomas scored 30 points, including 20 in the second half, and Boston beat the Miami Heat 112-108 on Sunday night for its fourth straight victory.
The win moved Boston within percentage points of Cleveland for the No. 1 seed in the East. The Celtics have one more victory than the Cavs, but also one more loss. Boston (48-26) also equaled its win total from last season.
Thomas said no one in a Celtics uniform was celebrating, though.
"It's just a tie, though, so it's not that cool," he said. "Hopefully we can secure that spot and be No. 1. We've just got to control what we can control and take it game by game. We can't really worry about what Cleveland's doing or what other teams are doing."
Jae Crowder added a season-high 25 points and six rebounds for the Celtics.
Hassan Whiteside finished with 19 points and 15 rebounds for Miami.
"I don't think it was the offense that really got us, that (is) inhibiting us from winning games," Tyler Johnson said. "I think it's getting stops down the stretch. We scored 108 points, so that's enough to get the job done."
Boston led by 10 entering the final period before letting Miami back into the game with an 8-0 run.
James Johnson hit one of two free throws to get the Heat within two with less than a minute to play. Then the Celtics' Marcus Smart got the benefit of a goaltending call on the second of his free throw attempts to put Boston up four with 20.1 seconds left.
The Celtics trailed by five at halftime, but outscored the Heat 32-17 in the third quarter.
Boston coach Brad Stevens was critical of his team's defensive effort late in a win over Phoenix on Friday, when Devin Booker scored 70 points for the Suns.
At one point in the second quarter Sunday, Stevens again chastised his club's performance on the defensive end as the Celtics fell into a 15-point hole.
They responded by closing out the final 7:09 of the half on a 25-15 run. They also closed the game with several big defensive plays, including an emphatic block by Al Horford on Tyler Johnson in the waning seconds.
"This is what happens with competition," Heat coach Erik Spoelstra said. "It's not only up to you. They have something to say about it as well. They just made some big, timely plays."
Heat: Whiteside had his 51st double-double of the season. ... Dion Waiters sat out with a sprained left ankle. Spoelstra said there is no timetable on Waiters' return.
Celtics: Thomas had his 65th game with 20-plus points this season, tying him with Oklahoma City's Russell Westbrook for most in the NBA. ... Thomas extended his franchise record to 48 consecutive games with a 3-pointer. ... Avery Bradley returned after missing a game with stomach flu. ... Crowder had his ninth 20-point game of the season.
Boston swept Miami in back-to-back seasons for the second time in franchise history. The first was 1988-89 and 1989-90.
FINAL FOUR TIES
At least two Miami players were scoreboard watching prior to Sunday's game. Heat veteran Udonis Haslem played for Final Four-bound South Carolina coach Frank Martin on three state championship teams at Miami Senior High in the late 1990s. Miami rookie Rodney McGruder also played for Martin for three years at Kansas State.
"The coach he played for, we tend to like Frank Martin players," Spoelstra said of McGruder, who has started 56 games. "They have the type of grit and the DNA, the toughness that we like."
Heat: At the Detroit Pistons on Tuesday.
Celtics: Host the Milwaukee Bucks on Wednesday.
Follow Kyle Hightower on Twitter at http://www.twitter.com/khightower
Daniel Jones' trip may not have been the worst we've seen
From the hardwood to the gridiron, SportsCenter relives some of the worst trips, slips and falls in professional sports.
Miami Heat president Pat Riley ready to run it back next season with similar team
Heat president Pat Riley enters the offseason with no intention of letting free agent Goran Dragic get away, and he wants to sign Bam Adebayo to an extension.
Sources: NBA eyes pre-Christmas start, 72-game regular season
Amid the pandemic, the NBA is proposing several changes to next season that includes a 72-game regular season, a play-in tournament and the likelihood of no All-Star Game in Indianapolis, sources said.