CLEVELAND — Royce Lewis' first home run was a grand slam, a rocket to right-center in Little League back in southern California.

"My dad loved that," Lewis recalled. "That's all he preached, going opposite field."

Fifteen years later, Lewis is still hitting them with astonishing frequency. Only difference is, now there's no 10-run surrender rule.

Lewis made major league history Monday by launching the fourth grand slam in his 56-game career and third in only eight days, his teammates added five more homers, and the Twins opened their AL Central "showdown" with the Guardians by inflicting a 20-6 farce at Progressive Field.

"He loves coming up with people on base," Twins manager Rocco Baldelli said of Lewis, the only rookie ever to collect four career slams, and only the fourth hitter in MLB history to hit three slams in an eight-game span. "He's not getting lucky. He's squaring a lot of balls up, and some of them are going over the fence. I hope he extends his record."

There were plenty of records on Monday — the most runs the Twins have ever scored in their 462 games in Cleveland, for instance — but the most important one to the Twins was: 73-66. That's their record, now six games ahead of the Guardians with 24 to play, close to a stranglehold on the AL Central crown.

Nearly as unbelievable as Lewis' second-inning blast with the bases loaded — he came up again in the sixth inning in the same situation, but merely singled home two more runs, giving him 10 RBI in the past two days — was who the slam came against.

Lucas Giolito was making his Guardians debut, after being acquired on waivers along with two other pitchers last week, in a last-ditch attempt to catch the Twins. But the longtime White Sox ace, who held the Twins to only two runs over 18 innings in three previous meetings this season, instead was pummeled.

Jorge Polanco homered in the first inning, Lewis connected in the second, and Carlos Correa hit one in the third inning, and Giolito, booed by Guardians fans as the rout went on, surrendered a career-high nine runs in only three innings.

No one did more damage than Lewis, though.

Giolito opened the second inning with back-to-back strikeouts, but then loaded the bases with two walks and Willi Castro's first hit since returning from the injured list. Polanco then drove home another run by drawing a walk, bringing up Lewis.

The rookie took two pitches in the dirt, then waited on something he could handle.

"He went down 2-0 so he has to come over the middle of the plate with something. Whether it was away or inside or something, I just chose to be picky in that situation," Lewis said. "I was just trying to look for a pitch over the plate, specifically a fastball middle-in, and he ended up throwing it right in that same tunnel I was looking in."

The game devolved into a farce by the end, with the Guardians turning to catcher David Fry to pitch in the sixth. He allowed seven runs over four innings, the longest pitching stint by a position player since Jose Oquendo in 1988, and allowed home runs to Joey Gallo, Kyle Farmer and Matt Wallner.

The Twins, meanwhile, turned to a position player of their own, Willi Castro, to pitch the ninth. He gave up three runs before retiring the side on Tyler Freeman's soft line drive to shortstop.

Pablo López was the recipient of the Twins' offensive outburst, though he was far from perfect. The righthander allowed eight hits — at least one in each of his six innings — and three walks. But only when José Ramirez followed a Steven Kwan single with a triple, one-hopping the wall in right-center with a López changeup, did the Twins starter give up a run.

"He muscled through it. He mentioned after I shook his hand, he goes, 'You know, I'm better than that,'" Baldelli said. "He wants the results, [but] he wants to feel like himself, in command of everything all the time."