Norris hit a three-run homer with two outs in the eighth inning, and the A's rallied to beat the Chicago Cubs 8-7 on Tuesday night to regain the AL West lead.
Five of the catcher's 11 career home runs have given Oakland the lead.
"He does his best work late in games with runners in scoring position," A's manager Bob Melvin said. "He's gotten big hits for us since he got here last year. If you're going to get a few hits in certain situations, obviously the bigger situations are the type of things that get the respect of your teammates and give us confidence when he comes up there in big situations he can get it done."
Norris, who entered the game with a .195 batting average backing up the injured John Jaso, sent the 2-2 changeup from James Russell (1-2) over the left-center field wall for his fourth home run this season. Josh Donaldson and Chris Young also homered to put the A's a half-game ahead of Texas, which lost 9-2 at Seattle.
Lefty Stephen Vogt would've started at catcher for the A's against Scott Feldman, but the Cubs traded the right-hander in the morning. When Norris showed up at the ballpark, he learned lefty Chris Rusin had been called up from Triple-A Iowa to take Feldman's place.
"I figured it was probably my turn," Norris said, grinning.
Alfonso Soriano hit a three-run homer to highlight a five-run fourth inning and Welington Castillo drove in three runs for Chicago, which twice blew a two-run lead. The Cubs are 35-46 at their season's midpoint after another win evaporated because the bullpen couldn't hold a lead.
"Just didn't make a good pitch when I needed to and paid for it," Russell said.
Oakland can once again thank its on-again, off-again catcher for a comeback. Besides his big home run, Norris threw out Luis Valbuena for a double play in the ninth when Balfour struck out Starlin Castro.
After tossing his first complete game to beat Homer Bailey and the Cincinnati Reds his last time out, A's starter A.J. Griffin gave up 10 hits and tied his career high with seven earned runs in 5 2/3 innings. Bailey threw his second career no-hitter Tuesday night to lead the Reds past the San Francisco Giants, 3-0.
"I'm just fortunate enough that I have a team that scores a ton of runs," Griffin said.
Rusin allowed six hits, struck out two and walked none in 3 1/3 innings for a no-decision in his first major league start this season. He was pitching on three days' rest, so Cubs manager Dale Sveum pulled Rusin after 61 pitches.
The A's roughed up Rusin at the outset.
Donaldson hit his 14th home run in the first, and Young followed with his eighth longball of the season in the second to give Oakland a 3-0 lead. The A's missed a chance to pile on -- and perhaps run Rusin out of the game even earlier -- when Jed Lowrie struck out with the bases loaded to end the second.
While Rusin regrouped in his short stint, so did Chicago's offense.
Soriano started the scoring burst when he sent the tying homer over the wall in center for his 10th home run. The Cubs sent 10 batters to the plate in the fourth inning, with Darwin Barney adding a sacrifice fly and Castillo hitting an RBI single to stretch Chicago's lead to 5-3.
The Cubs collapsed on defense in the bottom half behind Carlos Villanueva, who allowed two unearned runs in 3 1/3 innings of relief. Running back and to his right on Adam Rosales' short fly, shortstop Castro collided with Soriano in left field and the ball dropped. Coco Crisp followed with a tying, two-run single.
Castillo's two-run double over the head of Young in center put the Cubs back ahead, 7-5, and chased Griffin. But as has been the case so often this season, Chicago couldn't protect its lead.
"Just gotta get the ball down. It's that simple," Russell said. "It's not that difficult. It's just that one thing. Get the ball down and that won't happen."
Melvin said RHP Jarrod Parker felt a slight discomfort and tightness in his right hamstring during a bullpen session. Melvin said a decision will be made Wednesday on whether Parker, who left with the injury in the fourth inning of Saturday's loss against St. Louis, will make his next scheduled start Thursday against the Cubs. ... The Cubs had never played a regular-season game at the Oakland Coliseum. The franchise has now played in every current major league city and every active ballpark except the new Yankee Stadium. ... Bartolo Colon (11-2, 2.79 ERA) looks to win his ninth straight start when the A's face Matt Garza (3-1, 3.82 ERA) and the Cubs on Wednesday.