Jason Giambi and the rest of the Bronx Bombers figure to score plenty of runs this season, so even they know the biggest key to a big year stands 6-foot-10 and on the mound.

Randy Johnson rebounded from a poor outing and dominated Baltimore with ease, and Giambi homered twice and drove in five runs yesterday as the Yankees cruised to a 7-1 victory over the Orioles.

“You look up and down the lineup at all the big hitters, but we’re really going to ride the big fella,” Giambi said. “That’s what is going to take us into the postseason.”

Derek Jeter added three hits for the Yankees,who took two of three in the series. The Yankees have won 11 of 14 against Baltimore dating to last season.

Miguel Tejada homered and had all three hits off Johnson (3-2), roughed up in his previous start at Toronto.

“Early on he was a little flat with his slider. All of a sudden he started getting on top and putting people away,” manager Joe Torre said. “He was just about unhittable today.”

Pitching to Jorge Posada for the first time since opening day, Johnson tossed eight efficient innings with five strikeouts and one walk. Johnson normally uses backup Kelly Stinnett as his personal catcher, as he did with John Flaherty last season.

The Big Unit has won his last six decisions against the Orioles, who stacked their lineup with eight right-handed hitters to no avail.

“It’s a little tough to score when only one of your guys is getting base hits,” Baltimore manager Sam Perlozzo said. “Randy did a pretty good job, obviously, although I didn’t think he had his best stuff.”

The 42-year-old lefty threw 94 pitches and earned his 266th win, tying Hall of Famers Bob Feller and Eppa Rixey for 33rd place on baseball’s career list.

“Today he pitched like he was 22,”Baltimore third baseman Melvin Mora said.

Johnson was tagged for seven runs and nine hits in 3 1/3 innings of a 10-5 loss to the Blue Jays last Tuesday – the first time in 160 career starts he lost after having a four-run lead, according to the Elias Sports Bureau.

“You’re going to have some bad starts. I’m only human. It’s nice to be able to bounce back,” Johnson said. “There were some innings that were relatively easy, but by no means is that an easy lineup.”

The start was delayed 41 minutes by rain, but what began as a soggy day at Yankee Stadium turned sunny by the seventh inning.

Mariano Rivera worked the ninth and gave up a single to Tejada, who finished 4-for-4 with all four Orioles hits.

“I don’t feel so bad when he gets a base hit off Mo, too,” Johnson said.

Orioles starter Bruce Chen (0-3) allowed five runs – three earned – and 10 hits in four innings. He’s given up eight home runs in 20 2/3 innings this season.

Tejada homered off the left-field foul screen leading off the second.

Giambi, hitless in his previous nine atbats, opened the bottom half with a high liner over the right-center fence. No. 9 hitter Andy Phillips, making his third start of the year at first base, added a run-scoring single for his first RBI.

A two-out error by Mora on Alex Rodriguez’s grounder gave Giambi a chance to hit in the third. He drove a 3-2 pitch off the facade of the rightfield upper deck for his seventh homer and a 4-1 lead.

“This is the best I’ve felt in a while, putting on the Yankee uniform,” Giambi said. “My swing has felt good this year.”

Giambi came out for a curtain call for an announced crowd of 47,996 – though far fewer fans actually showed up in the rain. It was his 32nd career multihomer game and second in a week. He also connected twice last Sunday in Minnesota.

The Yankees loaded the bases with none out in the fifth, chasing Chen. Rodriguez’s sacrifice fly made it 5-1.

Giambi added a two-run double to the base of the left-field wall with two outs in the seventh off Jim Brower.

Second baseman Robinson Cano extended his team-high hitting streak to 12 games with two hits.