Smith blocked six shots in the second quarter, giving the Hawks momentum that carried them to a 96-91 win over the Philadelphia 76ers on Monday night.
He had 19 points, nine assists and nine blocks, and his big second quarter lifted the Hawks from a miserable start.
"Josh changes the game with his blocked shots," said 76ers coach Maurice Cheeks. "When a guy has nine blocked shots it changes the game dramatically. Even when he doesn't block a shot he has guys thinking about it when they shoot, and that can mess up your offensive rhythm."
The 76ers outscored the Hawks 15-0 on fastbreak points and outrebounded Atlanta 23-5 to take a 32-14 lead in the first quarter. Smith's second-quarter rejections fired up the Hawks, who outscored the 76ers 82-59 in the final three periods.
"Josh got really aggressive, just really made his presence felt in the paint," said Hawks center Al Horford. "He changed the game for us completely. He was carrying us in the second quarter."
Smith and the other starters struggled while falling behind by 20 in the first quarter.
"I understand when I came back in I had to change the game on the defensive end," Smith said.
"When you block a couple of shots, it makes them second-guess shots."
Smith, second in the league with 3.2 blocks per game, matched team records with the six blocks in the second quarter and eight in the first half.
"It felt great just to come over and help my teammates," Smith said. "Some of them turned into fast breaks."
Added Hawks coach Mike Woodson: "He changed the whole game. It's a shame that we put that kind of pressure on him. ... We just have to lock in and take the individual challenge to guard the ball. That's what we weren't doing, and he was covering up a lot of our mistakes."
Smith also had four steals and six rebounds in the game. Smith's career high is 10 blocked shots as a rookie against Dallas on Dec. 18, 2004.
Josh Childress scored 21 points and Joe Johnson added 18 for the Hawks.
Atlanta led 91-88 before turning the ball over on an offensive foul by Horford with 1:20 left. Philadelphia rookie Thaddeus Young, a Georgia Tech product making his first return to Atlanta, missed on the other end, and a basket by Horford pushed the Hawks' lead to five.
Horford then blocked a shot by Andre Miller, who scored 29 points.
"Al Horford makes a great block on Andre Miller at the end, which was huge," Woodson said. "He held his own and made the block and secured the ball. That was pretty much the game right there."
The Hawks set a season high with 14 blocks, including two by Horford.
Andre Iguodala's three-point play with 19.5 seconds to go cut Atlanta's lead to 94-91, but Smith answered with two free throws.
Iguodala had 22 points. Young added 11 and Willie Green had 10. Samuel Dalembert had nine points and 13 rebounds.
The 76ers' big early lead didn't last long. The Hawks outscored the 76ers 30-18 in the second quarter to trail only 50-44 at halftime.
The quick turnaround stunned the 76ers.
"I wish I could tell you what happened," said Dalembert.
"It was two games," Cheeks said.
Johnson's 3-pointer with four seconds left in the third put Atlanta in front 72-70 heading into the final quarter.
The Hawks led 87-79 in the fourth but the Sixers answered with two baskets by Miller and a 3-pointer by Iguodala to close the lead to 87-86 with 3:45 left.
A drive by Johnson with 1:53 left pushed Atlanta's lead to 91-88.
Wayne "Tree" Rollins blocked eight shots in a half for Atlanta against Cleveland on March 29, 1983, setting the record matched by Smith. ... 76ers executive vice president Larry Brown, who normally doesn't travel, attended the game. He said he made the trip to visit his brother Herb Brown, a Hawks assistant. Herb Brown and Woodson were assistants on Larry Brown's 2003-04 NBA championship Detroit team. ... Philadelphia F Jason Smith (left ankle sprain) did not play after testing the ankle before the game. ... Young made his third start, all in the last four games.