PHOENIX -- Junior Lake had a career-high four hits including his first major-league home run and left-hander Chris Rusin won an emergency start when the Chicago Cubs beat Arizona 4-2, hours after trading Matt Garza to Texas.
Lake, who was recalled from Triple-A Iowa on Friday, hit a two-run homer over the 413-foot sign to give the Cubs a 3-0 lead in the fifth inning. He also singled in the final run in the ninth and had two bunt singles. He has nine hits in his first 16 at-bats.
The Cubs' Dioner Navarro hit a bases-empty homer in the second.
Rusin (1-0) gave up only a single and a walk in five-plus innings after being recalled from Iowa to replace Garza, who was dealt to Texas for right-hander Justin Grimm, minor-league third baseman Mike Olt, minor-league right-hander C.J. Edwards and two players to be named later.
Kevin Gregg pitched a scoreless ninth for his 19th save for the Cubs (44-53), who had lost three of their last four.
Arizona (51-48) has lost four of its last five and fell out of first place in the NL West for the first time since May 17 when the Los Angeles Dodgers (51-47) beat Toronto 14-5 on Monday.
Didi Gregorius had three of the Diamondbacks' six hits and Paul Goldschmidt singled in a run for his 78th RBI of the season, one behind NL leader Brandon Phillips.
Rusin struck out four and walked two in his second start of the season.
Navarro's homer in the second inning was his ninth of the year, tying a career high he set with Tampa Bay in 2007. He was hit a pitch in the left knee in his next at-bat but showed no reaction, running swiftly to first.
Tyler Skaggs was back in the rotation after a short stint at Class A Visalia to get work during the All-Star break. Skaggs gave up three runs and struck out seven in six innings.
NOTES: Rusin was not caught completely off guard by his start. He flew to Phoenix from Round Rock, Texas, on Sunday night after Triple-A Iowa concluded its three-game series there, manager Dale Sveum said. ... RHP Brad Ziegler had Arizona's only save opportunity in San Francisco over the weekend and will stay in that role, Diamondbacks manager Kirk Gibson said. "Kind of make my decision as it goes on within the game, although I did tell 'Ziggy' the other day I was thinking he would be that guy. That's kind of where I am right now," Gibson said of the closer's role. The Diamondbacks have 19 blown saves, tied with the Cubs for the most in the majors. ... Cubs RF Cole Gillespie made a spectacular sliding catch of Aaron Hill's foul fly near the right field stands in the second inning. Gillespie's knees buckled as he slid into the padded wall while making the catch. ... The Diamondbacks could not help but look back at their loss to Milwaukee in the 2011 NLDS after Brewers OF Ryan Braun was suspended for the rest of the season Monday. "It's frustrating to know that maybe you were cheated on the other side of it a little bit," Diamondbacks IF/OF Willie Bloomquist said. Braun was 9-for-18 with four doubles, a home run and four RBIs in the NLDS, which the Brewers won in five games. He was suspended for 50-games after reportedly testing positive for elevated levels of testosterone in the winter of 2012, but the suspension was overturned after his appeal. ... Arizona optioned LHP Eury De La Rosa to Triple-A Reno after recalling Skaggs for the start, De La Rosa retired all seven batters he faced in two appearances.