CHICAGO -- It has been nearly five years since Chris Bassitt last wore a White Sox uniform, but the sting of being dumped by his original team remains intense for the 30-year-old right-hander.

“Every time I pitch against these guys for my career, I’m gonna try to prove to them they made a mistake,” he said. “That’s the reality of it. Anyone who says different is lying.

“Anytime I’m pitching against these guys, they’re gonna get my ‘A’ game.”

• Box score

Bassitt certainly had his ‘A’ game on Sunday, tossing seven shutout innings to outduel Lucas Giolito and lead the A’s to a 2-0 shutout of the White Sox in the rubber game of the three-game series at Guaranteed Rate Field.

Overall, the A’s split their six-game stay in Chicago. They dropped two of three to the Cubs at Wrigley Field before moving to the South Side.

Bassitt (8-5) allowed just four hits while striking out seven and walking two. Jake Diekman and Joakim Soria combined for a scoreless eighth, and Liam Hendriks got the final three outs for his 12th save.

Bassitt is 3-1 with a 2.00 ERA in six starts since the All-Star break.

“I think I’ve said a couple of times this season, 'That might be the best game I’ve seen him pitch,' but that one ranks right up there,’’ A’s manager Bob Melvin said. “Coming back home, pitching against your former team, after losing one [Saturday] night, I know he was up for the challenge.”

Bassitt also was up for the challenge of facing Giolito.

“You go into this game knowing you better bring your good stuff,” Bassitt said. “He’s obviously an All-Star, but he’s got tremendous stuff.”

Giolito (12-6) had a career-high 13 strikeouts, but he took the loss after allowing two runs on five hits in six innings.

The A’s did all of their damage against Giolito in the fourth. Matt Chapman led off with a drive that seemed headed out of the ballpark before right fielder Jon Jay reached over the fence and got a glove on it. Jay couldn’t secure the catch, but he knocked the ball back onto the field, and Chapman had to settle for a double.

Matt Olson then homered over the right-field bullpen -- and out of Jay’s reach -- for a 2-0 Oakland lead.

“That’s kind of how you have to beat him, is maybe string a couple of hits together and someone hits a homer,” Melvin said.

Bassitt, who was drafted by Chicago in 2011, made his debut in the Major Leagues in August 2014. He pitched in six games (five starts) that season, going 1-1 with a 3.94 ERA.

Bassitt joined the A’s organization the following year and underwent Tommy John surgery in 2016. He didn’t pitch at all in 2017 before returning to action last season. Before this season, he had an unspectacular 2-14 record in the Majors.

This has been a breakout season for Bassitt, which has picked up since he added a changeup to his arsenal after being roughed up for six runs in 4 1/3 innings July 6 at Seattle.

“Sometimes, really bad outings are exactly what you need, and I truly believe that Seattle thing was exactly the kick in the butt I needed,” Bassitt said. “‘Hey, you need a changeup.’ Today it saved me. I got a couple of big outs on changeups.”

Bassitt's biggest jam came in the second, when he was aided by good defense and bad baserunning. Chicago’s Eloy Jimenez led off with a walk, and Matt Skole followed with an infield single. Yolmer Sanchez then hit a deep fly to right. Jimenez tagged up and went to third. Skole also tried to tag up, but he was thrown out 9-6-4 for the second out.

Bassitt then struck out Ryan Goins to end the threat.