The 23-year-old right-hander justified that confidence once again.
"It's never an easy game when we play them," Girardi said about Baltimore. "They're a very good team and they're very explosive. You never really feel it's safe."
The Yankees can hand Baltimore just its second series loss at Camden Yards this season in the finale Wednesday. The Orioles have been hampered by their starting pitching and lost eight of their past nine games.
Severino (4-2) allowed one run on seven hits with eight strikeouts over 6 1/3 innings. He has given up three or fewer runs in each of his past five starts and has been a key for New York's resurgence.
Gardner set the tone for the Yankees when he hammered Chris Tillman's third pitch of the game over the right-field fence. It was his eighth career leadoff homer. Two batters later, Holliday hit another solo shot and Baltimore never recovered.
Gardner and Holliday have 11 home runs apiece on the season.
"When you have a guy up and down the lineup that can hit homers, it puts a lot of pressure on the other team," Holliday said. "Having a guy that can start the game with a home run is a nice weapon."
Aaron Hicks boosted the lead to 3-0 with an RBI single in the second, and Holliday added another run with his second homer an inning later.
Chase Headley gave New York a 5-0 lead with an RBI single in the third that chased Tillman (1-2), who has pitched past the fifth inning just once in five starts.
"They came out hacking and you were falling behind," Tillman said. "You're not putting yourself in good position to get the results you're looking for."
New York continued to pound Baltimore's pitchers, and Gardner got his second home run off Logan Verrett in the fourth. Later that inning, rookie Aaron Judge, who leads the team with 37 RBIs, increased the lead to 8-0 with a two-run double.
Trey Mancini managed three hits and gave the Orioles their first run with an infield single in the sixth. Joey Rickard and J.J. Hardy each had an RBI single in the eighth off Bryan Mitchell.
"Most of these games have been very close," Mancini said. "Sometimes, I think the pitching and hitting haven't matched up. A lot of the times maybe when the pitchers are doing well, the (hitters) are slacking a little bit and maybe vice-versa, but that's baseball, and that's going to happen a lot in the course of the season."
NOTES: Baltimore RHP Alec Asher (1-3) will start Friday against the Red Sox despite struggling in his previous outing. He allowed six runs on six hits over just two innings Sunday against the Astros. The Orioles will keep RHP Ubaldo Jimenez in the bullpen. ... Yankees CF Jacoby Ellsbury (concussion, sprained neck) was expected to do some running Tuesday and then possibly hit in the cage, manager Joe Girardi said. ... Orioles CF Adam Jones, who has been dealing with soreness in his left ankle and hip, missed his fourth straight game. An Orioles spokesman said Jones was held out because of the wet field conditions.