The Heat (27-11) have lost three consecutive games for the first time in two seasons.
They have had uncharacteristic defensive shortcomings during the losing streak.
"We just need to get connected," Heat coach Erik Spoelstra said after Wednesday's loss. "It's not a matter of knowing what we do, knowing where we go. It's a matter of connecting and doing it. That's really it.
"And we'll take care of it as we move forward."
It didn't take long to realize the Heat would have a tough time guarding the Wizards. Washington scored 16 fast-break points while leading 43-18 after one quarter. The Wizards scored 69 first-half points and led by as many as 34 points in the game.
"You just can slide this one under the rug," Spoelstra said. "That won't benefit us."
But a win over Miami would mark the first time the Sixers (13-25) won consecutive series games over the Heat since winning five straight on Jan. 19, 2007 to Feb. 23, 2008.
The Sixers stunned Miami in this season's opening game, but the Heat were a night removed from beating the Bulls in Miami. The Heat were also without all-star Dwyane Wade, who got the night off.
That game served as the coming-out party for Michael Carter-Williams. The Sixers rookie point guard finished with 22 points, 12 assists, nine steals and seven rebounds. His nine steals were an NBA record for a rookie in his first game.
"They want to get back on the winning side or the fact that we played with some success when we played them last," Brown said, "all those things, throw them anywhere you want. At the end of the day, we are just playing against a well-coached team with a lot of talent."