BOSTON -- "These teams don't like each other."

You've heard the cliche thousands of times if you're a sports fan. Sometimes it's justified. Sometimes it's a bit overblown.

The Washington Wizards and Boston Celtics, who open their Eastern Conference semifinal series on Sunday at TD Garden, really don't like each other.

The season series between the teams, even at 2-2 (both teams winning their two home games), featured all kinds of rudeness, some of it even threatening to pour off the court -- as members of the Boston police stood in the hallway between the locker rooms after one game.

The Wizards even wore black to a home game against the Celtics.

But Washington guard Bradley Beal, talking to reporters Saturday, said, "It's basketball -- we're not fighting out here ... gonna keep it clean."

Now, whether or not the teams can do anything really mean to each other Sunday could be in doubt because they could be too tired to do anything but play basketball.

Both wrapped up their first-round series with Game 6 wins on Friday night and now have to play again some 40 hours later.

And on the Boston side, top scorer Isaiah Thomas flew from Chicago to Tacoma, Wash., for his sister's funeral and is due back in time for the game.

Celtics coach Brad Stevens made it clear Friday night he was not requiring his best player to get back for the game. But Thomas, who played the entire first round just after his sister's passing, is expected back.

"His plan is to come back today," Stevens told reporters at Saturday's practice. "But like I said last night, if it becomes too much and he needs to stay, whatever he needs."

On Friday, Stevens said, "Tomorrow's a lot more important than Sunday."

Team president Danny Ainge and assistant coach Jerome Allen accompanied Thomas to the Pacific Northwest.

"If we would have played Tuesday, I was gone, I was going," Stevens said. "With this turnaround, Danny went, Jerome Allen went out there. We all send our best. It's hard to think about how he feels right now."

Thomas' teammate, Avery Bradley, who also grew up in Tacoma, said members of his family would represent him at the funeral.

Thomas averaged 27.8 points per game against the Wizards and their talented backcourt this season.

On the other side, John Wall averaged 17.8 points and 8.3 rebounds but shot just 37.3 percent from the floor and 15.4 percent on 3-pointers against Boston. Beal scored 22 per game while shooting 47.8 percent overall and from behind the arc. Backup Kelly Oubre Jr. has done a good job defending Thomas this season.

Washington's Otto Porter Jr. played well against Boston, averaging 17 points and 6.8 rebounds per game and notching 34/14 while hitting 14 of 19 shots in one win. He has helped the Wizards control the boards against the Celtics.

Wall and Beal, who could be the most talented guard tandem in the league, combined for 73 points in the elimination win Friday night.

Wall, who averaged 29.5 points and 10.3 assists in the series against Atlanta, scored 19 fourth-quarter points and had a huge block as the Wizards blew 19 of a 22-point lead before Wall made sure they didn't blow it and force Game 7.

"We've been in this situation before, but we probably didn't have the confidence to close like we did late in the game," Wall said. "Now we do."

The Wizards will have to do it without Ian Mahinmi for at least Game 1. He remains out with a calf injury after missing the entire first round.