ATLANTA — The Atlanta Hawks just won't let go of their first trip to the postseason in nine years.

The playoff team with the worst record did it again to the team with the best mark, forcing an improbable Game 7 with the Boston Celtics, as Joe Johnson hit a crucial 3-pointer with 1:07 remaining and the Hawks held on for a 103-100 victory tonight.

The Hawks, just 37-45 during the regular season, have now beaten the Celtics three times in the space of a week to set up a deciding game in a series that was supposed to be a sweep. After all, Boston went an NBA-leading 66-16 and defeated Atlanta in all three meetings before the playoffs.

But, against all odds, the Hawks are heading to Boston for Game 7 on Sunday.

"Seven! Seven! Seven!" chanted the record crowd of 20,425 at Philips Arena.

The Celtics are still the favorite, having won all three games on their home court in the series by an average of 22 points. But the Hawks have lasted longer than anyone would have expected.

Marvin Williams led the Hawks with 18 points despite missing much of the fourth quarter with a sprained left knee. Kevin Garnett had 22 for the Celtics and Ray Allen added 20, but Paul Pierce — the other member of Boston's Big Three — fouled out on a disputed call in the fourth quarter.

The Celtics had a chance after pounding the boards for five chances on one possession before Kendrick Perkins was fouled by Al Horford. Perkins made both free throws with 1:32 left to pull Boston within 97-95.

Johnson, who went to the final period with just seven points on 3-of-9 shooting, came alive in the fourth. He saved his biggest shot for the end, getting James Posey in the air with a pump fake before hitting Atlanta's only 3-pointer of the game to make it 100-95.

Pierce sat on the bench with a towel over his head, unable to watch.

Posey got Johnson back by hitting a tough 3 from the wing with 48 seconds left, and the Celtics had a chance when Johnson missed a runner in the lane.

Wanting to finish off the pesky Hawks, the Celtics drew up a play to give Allen a look from beyond the arc. He missed, though; Johnson grabbed the rebound, was fouled and hit two free throws with 10.6 seconds left.

After a quick basket by Garnett, Mike Bibby made only one of two free throws with 7.4 seconds to go, giving the Celtics a shot at forcing overtime. But the Hawks kept the ball from Allen and Posey, forcing Rajon Rondo to launch a long 3 that didn't even hit the rim as the horn sounded.

For the third time in the series, streamers poured from the Philips Arena rafters. Zaza Pachulia, who played a key role off the bench, grabbed a microphone to salute the joyous crowd.

"We're going to Game 7! Woooooooooo!" he screamed.