Amed Rosario and Andres Gimenez also hit two-run homers, while Jose Ramirez and Bo Naylor each had an RBI double for the Guardians, who snapped a four-game losing streak
Cleveland's Xzavion Curry, making his first start of the season in what was a bullpen game, pitched three scoreless innings. He allowed one hit and one walk, striking out two.
Michael Kelly (1-0) pitched 1 2/3 innings to earn the win. He allowed two hits and fanned two.
The Pirates have lost four games in a row and eight of their last nine
Pittsburgh starter Quinn Priester (0-1), making his major league debut, gave up seven runs and seven hits in 5 1/3 innings, with two strikeouts and two walks.
Pittsburgh's starting lineup featured six rookies, with Priester's batterymate and fellow touted prospect, Endy Rodriguez, also making his big-league debut.
Priester was perfect through three innings, with eight of his nine outs coming on ground balls.
In the fourth, Steven Kwan led off with a walk. Rosario followed with his third homer of the season for a 2-0 Cleveland lead.
With one out in the fifth, Priester walked Will Brennan. An out later, Bo Naylor doubled to left center, driving in Brennan to make it 3-0.
Rosario singled to shallow center to lead off the sixth. Ramirez knocked him in with a double off the wall in right. Josh Naylor's double brought Ramirez home to make it 5-0. Gimenez then extended the lead with his two-run blast to right.
In the seventh, Kwan got hit by pitch. Two outs later, Josh Naylor hit his 13th homer as the Guardians went up 9-0
Josh Bell got hit by a pitch in the eighth, went to third on Myles Straw's one-out double and scored on Kwan's two-out single that pushed the lead to 10.
Straw's bases-loaded infield single in the ninth completed the scoring.
First pitch was delayed for 47 minutes because of rain.
--Field Level Media