CHICAGO -- Willson Contreras watched the baseball soar over left field as he walked briskly up the first-base line. When the ball found the basket, then came the emphatic flip of the bat and the raucous eruption from Cubs fans at Wrigley Field.

In the first inning of Wednesday’s 7-3 win over the White Sox, Contreras electrified his audience with a grand slam off White Sox starter Lucas Giolito, whose Cy Young-level production hit a snag on the North Side. It was the first of two home runs by the Cubs catcher against Giolito within the game's first three innings, and the timing of the moment was special for Contreras.

The blast came three years to the day of Contreras' first home run in his first Major League at-bat.

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"It makes me proud to look back and see how far I have come," Contreras said, "and how good this team is to me."

Contreras had his fingerprints all over the win, which moved the Cubs a half-game ahead of the Brewers atop the National League Central. Not only did he belt the pair of homers, but the catcher guided veteran Jon Lester through a gutsy 114-pitch performance. And in the fifth, Contreras showed off his arm by throwing out Tim Anderson on a would-be steal of third base.

Those three components factor into Contreras currently being the leading vote-getter at his position in NL All-Star balloting. If he stays atop that list, he will become the first Cubs catcher to start consecutive All-Star Games since Hall of Famer Gabby Hartnett in 1936-37.

"You could tell last year he was going through some learning," Lester said, "of how to catch every day and be at the big league level and perform and put up what we all know Willy can do. And this year he's doing it again. I think he's just learned how to manage his body and manage his time behind the plate. And we're seeing that on the offensive side, which is awesome for us."

Contreras joined Aramis Ramirez as the only Cubs players to have at least two multi-homer games against the White Sox. Contreras also belted two shots -- including a first-inning grand slam, as it happens -- and collected seven RBIs against the South Siders on May 11 of last season.

A smile crept across Contreras' face when asked about that previous slam.

"It's crazy. It's crazy," he said. "That came to my mind. It was last year against them. But today I think is more special."

That showing last year by Contreras came against a pair of White Sox pitchers -- neither of the caliber of Giolito this year. Giolito gave up four runs on one pitch after having not allowed four earned runs in a start since April 12, and the righty had not given up at least five since April 6. He had not surrendered two home runs in the same game since Sept. 10 of last season.

In fact, Giolito entered Wednesday having allowed just six earned runs over his previous eight outings, in which he went 8-0 with a 0.94 ERA with 65 strikeouts, 14 walks and two homers allowed in 57 1/3 innings.

"Contreras' homer, we needed that at that point to really gain some separation," Cubs manager Joe Maddon said. "I could see where Giolito's really reinvented himself. The arm stroke, the stuff that he's got. It's a different commodity than I saw last time. There's no question. So you need to throw that shot early, which we did, which was great."

David Bote added a solo shot in the fourth off Giolito, who exited with six runs against him in 4 1/3 innings. The three homers were his most allowed in a game since July 3 of last season.

Leading up to Contreras' slam, Giolito allowed a double to Kyle Schwarber before later issuing a pair of one-out walks. That set the stage for Contreras, who drilled a 1-2 changeup out to left field. Contreras shouted as he rounded first, pointed to the sky after rounding third and then saluted the crowd before heading back into the Cubs' dugout.

"Just hung it, left it up in the zone a little bit," Giolito said. "He caught it out in front. I've gotten away with that pitch before, but he probably had a better approach to it. I've got to be better, got to get that pitch down."

Then, Contreras pounded an 0-1 fastball in the third inning -- a rocket shot measured at 112 mph off the bat by Statcast -- sending it into the left-field bleacher seats. That blast gave the Cubs a 5-1 advantage at the time and marked Contreras' 15th home run of the season.

Contreras is now batting .293 with 42 RBIs and a 146 wRC+, indicating that he has performed 46 percent above league average as a hitter. Last year, Contreras posted a 100 wRC+ overall, but slumped to the tune of a .185 average and .553 OPS over the season's final two months.

"It's been good to watch," Maddon said of Contreras' turnaround. "He's been consistent with his batting -- his stance, etc. -- it's been consistent. And I think you're seeing the residue of that -- the ball being struck. ... He's becoming more self aware. I think that's the difference. He hits the ball hard."