The two teams went down to the wire again, coming off the third highest scoring game in NBA history.
The Hawks had to sweat out this one after leading most of the way.
Markkanen hit two free throws to cut it to 118-117 with 1:14 remaining before Atlanta's Kevin Huerter answered with a floater. With fans ready to let out a deafening roar, Dunn missed a wide-open 3 from the wing with 21 seconds remaining.
Huerter then missed two free throws with 15.7 seconds left. Chicago's Wayne Selden got the rebound. But after a timeout, Markkanen missed a 3 from the top of the key.
The Hawks’ Kent Bazemore got the rebound, then hit one of two free throws to make it a four-point game with 7.7 seconds remaining.
The Hawks were without three players.
Forward John Collins missed his second game in a row because of flu-like symptoms and did not travel with the team.
Omari Spellman could miss the remainder of the season because of a high left ankle sprain suffered in Friday's loss. He had an MRI on Saturday. The Hawks said he will be re-evaluated in a month, and coach Lloyd Pierce wasn't sure if Spellman will return this season. "That one's tough," Pierce said. "He sprained it very (badly). It's a legit ordeal."
Taurean Prince, awaiting the birth of his second child, missed the game.
The Hawks play at Miami Monday night.