PHILADELPHIA -- Two pitches were all it took for the Chicago Cubs to have to change their game plan at the plate.

Right-handed starter Vince Velasquez of the Philadelphia Phillies, whose fastball is usually in the mid-90s, threw two pitchers topping out at 87 mph to start the game and left because of what manager Pete Mackanin after the game called a strained right bicep.

Velasquez was relieved by left-hander Brett Oberholtzer.

"Everything you planned before the game changes ... especially when you go (from) right (handed) to left," Cubs manager Joe Maddon said. "And he's an entirely different pitcher."

After Oberholtzer gave a valiant effort in a pinch, the Cubs finally got to the Phillies bullpen in the sixth inning and earned an 8-1 victory at Citizens Bank Park behind a dominant effort from John Lackey.

Oberholtzer threw four innings, allowing one unearned run.

Bailey served up two 400-plus foot home runs in the sixth as Chicago seized control of the game.

With the Cubs leading 1-0, Phillies reliever Andrew Bailey served up two 400-plus foot home runs in the sixth.

The first came off the bat of Kris Bryant with Jason Heyward on base after a leadoff single. The Cubs third baseman belted Bailey's 2-and-2 fastball 432 feet into the left field seats for his 14th home run of the season.

Two batters later, Ben Zobrist ripped a 2-and-1 cutter 413 feet in right center to put the Cubs ahead 4-0.

The way Lackey was throwing, that was more than plenty of runs for Chicago.

The right-hander held the Phillies to three hits through seven shutout innings, with eight strikeouts and no walks.

"He just attacked our weaknesses," Mackanin said.

Lackey retired 16 straight Phillies after a Cody Asche single with two outs in the second.

"We kind of got a sense of how they were going to approach us early on," Lackey said. "And (catcher Miguel Montero) and I talked after the first inning and made some adjustments and things started rolling."

That number reached 19 straight Phillies retired after an inning of shutdown relief from Pedro Strop.

Clayton Richard walked Tommy Joseph to lead off the ninth, the Phillies' first base runner since Asche's single, and he later scored on a groundout by Cesar Hernandez.

Philadelphia (29-31) nearly got to Lackey in the first inning. Odubel Herrera and Hernandez led off with back-to-back singles, with Herrera advancing to third on Hernandez's hit.

But Freddy Galvis flied out to left fielder Albert Almora Jr., who made his first major league start, and Almora showed off his arm, cutting down Herrera at the plate for a double play.

"That was a big play," Maddon said. "That took anything away from them, momentum-wise… He just threw a bullet."

The Cubs (41-17), who totaled 13 hits, scored four runs in the eighth against Phillies reliever Colton Murray.

Almora Jr. registered his first big league hit, a RBI single to make it 6-0. Javier Baez, who was 4-for-4 with three RBIs, made it 8-0 with a two-run single.

"More than anything, on a day like today, John Lackey was the reason why that game turned out as well as it did," Maddon said.

Mackanin said Velasquez, 24, will be reevaluated tomorrow.

"His third to last pitch in his warm up, he felt something," Mackanin said. "The trainers recommended he go out and throw a couple pitches and see how he felt. When I saw (the velocity), we decided to get him out."

NOTES: First pitch in Wednesday's Phillies-Cubs game was delayed briefly by rain. ... Phillies 1B Ryan Howard, who is the assumed backup to Tommy Joseph, started for the second straight game. ... Chicago RHP John Lackey pitched in his 400th career game Wednesday. His next start will be his 400th career start. ... With 2012 first-round pick, OF Albert Almora Jr., debuting for Chicago on Tuesday, the Cubs have had their first-round selections from the 2011 (Javier Baez), 2012, 2013 (Kris Bryant) and 2014 (Kyle Schwarber) drafts play this season. ... The Phillies will pick first in Thursday night's MLB draft for the second time in franchise history.