ATLANTA - The final seconds of Celtics’ playoff games at Philips Arena have not been Rajon Rondo’s best moments.

In Game 1, Rondo bumped into official Marc Davis, leading to an ejection and suspension. In Game 5 Tuesday night, Rondo ran into the Hawks’ Al Horford and failed to get off a shot as the Celtics fell, 87-86, cutting their series advantage to 3-2.

Rondo did have showcase moments Tuesday, but the Celtics struggled with matchups as Horford returned for his second appearance since Jan. 11 and Marvin Williams provided physical defending and a 3-point threat.

So, the Celtics were unable to take advantage of the momentum gained by their breakout performance two days earlier and failed to convert in crunch time, extending the series to Game 6 at the TD Garden Thursday.

“Overall, I thought they played harder and better than us,’’ Celtics coach Doc Rivers said of the Hawks. “When you look at the last couple of games, we had great motion and movement. But I don’t think we had any of that tonight. I thought we were a stagnant basketball team.

“It was good in the first quarter - we missed a lot of open shots - but then things changed. They had a lot of open shots they missed, but then they started making them and got their confidence up.’’

But the Hawks would not likely have maintained that confidence without Horford’s inspiration and shot-making.

Horford, who missed the final 55 games of the season recovering from pectoral surgery, made a brief return during the Celtics’ 101-79 victory in Game 4. But Horford was in postseason form as he went for 19 points and 11 rebounds in 41 minutes.

“Listen, this was the team they thought they were going to start the season with and now they have it,’’ Rivers said. “So now we have to deal with it.’’

Actually, the Hawks are still missing center Zaza Pachulia (ankle), who could end up playing, according to coach Larry Drew.