Hairston hit a grand slam and Garza got his first victory of the season and the Cubs extended their winning streak to five games by defeating the Arizona Diamondbacks 7-2 on Friday.
Alfonso Soriano had a two-run homer and Cody Ransom added a solo shot for the Cubs, who scored all their runs on homers and have won five straight for the first time since winning seven in a row from July 31-Aug. 6, 2011.
The Cubs are still in fourth place in the NL Central, but they've shown signs of a turnaround.
Starting with a comeback 5-4 win last Sunday at Cincinnati that ended a six-game skid, Chicago has outscored opponents 36-12 and has a plus-11 run differential, which is seventh-best in the National League.
"We're playing catch-up to everyone else but the fact of the matter is it's still a long season," Cubs manager Dale Sveum said.
"You've seen it before when teams can win 15 in a row, 14 out of 16 something like that and all of a sudden before you know it you're right back in it and starting to have a lot of fun."
The Cubs had plenty of fun Friday, and the win looked similar to their three victories over the White Sox when they outscored their rivals 24-6.
Hairston's grand slam was the second in two games for the Cubs and was the highlight of a five-run third off Arizona starter Wade Miley (3-5).
Pitcher Travis Wood hit one on Thursday in a win over the White Sox. It also gave them grand slams in consecutive games at Wrigley Field for the first time since Jim Hickman and Burt Hooton did it Sept. 15-16, 1972, against the Mets.
"I think confidence has a lot to do with it," Hairston said. "The weather's getting warmer and the wind's blowing out. It makes you feel better as a hitter."
Garza (1-0), who was also making his first home start of the season, bounced back from his previous start, when he gave up four runs in four innings last Sunday in Cincinnati.
In his third start of the season since coming off the disabled list with a strained back muscle, Garza pitched seven innings and allowed two runs and six hits while striking out four for his first victory since July 15 of last season.
"I'm pumped to get it out of the way. Yeah, it's huge," Garza said. "But just glad I kept this thing rolling."
Things didn't go nearly as well for Miley and the Diamondbacks.
Soriano gave the Cubs a 2-0 lead in the first with a two-run home run. On a 1-1 pitch, Soriano hit a high drive that was helped by the wind blowing out. The homer was Soriano's 378th of his career, tying him with Diamondbacks third-base coach Matt Williams for 66th all time.
The Cubs then scored five runs in the third on Hairston's grand slam and Ransom's solo homer to cap the inning, which equaled their fourth inning against Texas on May 6 as Chicago's biggest of the year.
One year after winning 16 games and finishing second in NL Rookie of the Year voting, Miley continued to struggle, going seven innings and allowing seven runs and seven hits. He's lost four straight decisions and has given up 22 earned runs over his past four starts.
"Pretty frustrated. But you gotta take those four innings, I feel like that's more me. I gotta move on from there," Miley said. "Throw the other stuff behind me, quit thinking, get the mental stuff out of my head and just go pitch, you know, compete."
Miley's tough start was the second in a row for Arizona, which has lost four straight on the road. On Thursday, Brandon McCarthy lasted 2 2/3 innings and allowed nine hits and six runs in a 9-5 loss to the Rangers.
Arizona manager Kirk Gibson wasn't focusing on how Miley helped save a taxed bullpen, just the seven early runs.
"Well, we're not here to save our bullpen, we're here to win games," Gibson said. "He didn't throw the ball very good, made some mistakes."
The Cubs capitalized. Combining the offense with the effective starting pitching and a defense that helped Garza, including a catch by Hairston against the ivy on a Paul Goldschmidt drive in the first, Chicago had another easy win.
"It was a great team effort today, through and through," Hairston said.
Soriano's home run was his 18th in his 145th career at-bat against Arizona. ... Garza went 0 for 3 at the plate to keeping Cubs pitchers at 19 RBIs in May, the most by a pitching staff during one month in NL history. ... The announced attendance of 24,645 was the smallest of the season at Wrigley Field. ... The umpiring crew at Wrigley Field also worked Thursday's Royals-Cardinals game in St. Louis that ended at 3:14 a.m. Friday. ... Before Friday's game the Diamondbacks placed 3B Eric Chavez on the 15-day disabled list with a strained oblique he suffered Thursday at Texas. Arizona also activated utility man Willie Bloomquist from the DL after missing two months with an oblique strain. ... Saturday's pitching matchup is the Diamondbacks' Ian Kennedy (2-3, 4.70) against the Cubs' Jeff Samardzija (3-6, 2.85).