CINCINNATI -- Resulting from adjustments he made over the winter, Jason Heyward's swing is edging closer to the 2012 version when he produced career highs in home runs and RBIs with Atlanta. With Heyward producing in the lower half of the lineup, the Chicago Cubs' offense has boundless potential.

On Saturday, Willson Contreras hit his first career grand slam and Anthony Rizzo and Heyward each hit three-run shots, lifting the Cubs to a 12-8 victory over the Cincinnati Reds on a chilly afternoon at Great American Ball Park.

Contreras went 3-for-4 with a double, four RBIs and four runs. Heyward also had four RBIs. Coming off a season in which he had career lows in homers and RBIs and batted .230, Heyward is finding his stride.

"The signs are getting base hits," Heyward said. "The homers are going to happen. But it's not going to happen if you're not making solid contact. Being aggressive in the zone and lay off the bad pitches."

The home run barrage helped Jake Arrieta (3-0) earn the victory despite allowing four runs in the first. Arrieta struck out eight and didn't walk a batter, but allowed five earned runs and a pair of home runs.

"The velocity looked a little better," Cubs manager Joe Maddon said. "The slider was better today. He threw the ball better, just had one bad inning."

The Cubs (10-7) have won four straight and 20 of 24 against the Reds (9-9), who've lost four in a row.

Joey Votto hit a three-run homer and Eugenio Suarez hit a solo shot to briefly put Cincinnati ahead in the first. Suarez added a solo shot in the eighth off Justin Grimm to snap a 14 2/3-inning scoreless streak for Chicago's bullpen.

With a game-time temperature of 51 degrees, Saturday seemed like a good day to pitch, but it didn't turn out that way.

Rizzo, who hit a game-tying three-run home run in the ninth inning on Friday night, picked up where he left off on Saturday, launching Cody Reed's 1-1 pitch into the home bullpen in right field to put the Cubs ahead 3-0.

"The ball was in the air today," said Maddon.

Rizzo's blast followed consecutive walks by Reed to begin the game after he had retired all 18 batters he faced with seven strikeouts over his previous three games.

Votto's three-run blast to right-center tied the score in the bottom half of the first. He had five RBIs on Saturday.

Suarez put Cincinnati ahead 4-3 with his fourth homer two batters later. But, Reed couldn't hold the lead.

"I've had good starts before," Reed said. "I'm just not executing what I need to do. We score, what, (eight) runs and we lose? That's tough."

Reed (1-1) had five full counts and walked five batters in his two innings. He was charged with seven earned runs and allowed two homers.

"He didn't throw it nearly as well today as he had been," said Reds manager Bryan Price. "It's hard to ask your bullpen to come in and go seven scoreless. It's hard to overcome two three-run homers and a grand slam."

Arrieta found his stride after allowing four runs on two homers in the first inning. He'd given up seven runs and one homer in the first over 57 previous starts combined.

"The one mistake today was the cutter in to Votto," Arrieta said. "He's a guy who you just can't miss in certain spots and that's one of them. After that point, I was able to lock it in. Command was actually really good. Maybe the best I've had all year."

Reed's struggled continued into the second inning when, with two outs, the Cubs loaded the bases on a double by Kris Bryant and a pair of walks. Contreras then crushed the first pitch for a grand slam and a 7-4 lead.

Arrieta tripled in a run in the fifth inning to make the score 8-5. Heyward made it 11-5 when he crushed a 1-2 pitch for a three-run home run off right-hander Lisalverto Bonilla in the sixth. It was Heyward's second homer this season.

Bonilla pitched five innings in relief for Cincinnati, allowing four runs.

Heyward also turned in a key defensive play when he raced in to make a sliding grab on Zack Cozart's sinking liner and then doubled Suarez off first.

"I was expecting it to happen, I saw the hit-and-run," Heyward said. "I knew I had a pretty good jump on it. It's always cool to be able to double him off and get out of the inning."

NOTES: Cubs INF Tommy La Stella was reinstated from the bereavement list on Saturday and optioned to Triple-A Iowa. ... Reds CF Billy Hamilton was given a day off on Saturday. Scott Schebler started in center. ... Cubs INF/OF Ben Zobrist was out of the lineup for the third straight day with back tightness. ... According to STATS, the Cubs won three straight games in which they trailed by three or more runs in each for the first time since July 24-26, 1929.