Arizona Diamondbacks rookie left-hander Tyler Skaggs made two mistakes Monday night and they both ended up costing him.

"I just panicked," Skaggs said of an errant throw to first that helped lead to a 3-2 loss to the Cincinnati Reds. "I made a stupid play that cost us the ballgame."

Skaggs was poised to escape a bases-loaded situation without allowing a run when Wilson Valdez chopped a ball back to the mound. The rookie snared the ball but his throw to Paul Goldschmidt went in and out of the first baseman's glove and toward the Reds' dugout, allowing Scott Rolen to score from third.

Goldschmidt was tagged with the error but Skaggs accepted the blame.

"I threw away the ball," Skaggs said. "A lot of things went wrong on that play. I just rushed in my head and Paul wasn't there yet and I just panicked because I knew he was fast."

Skaggs' second mistake came in the sixth, when he left a four-seam fastball over the plate on the eighth pitch of an at-bat against Reds starter Bronson Arroyo.

Arroyo, who already had fouled two pitches straight back, lofted a pitch from Tyler Skaggs toward the left-field bleachers where it struck a railing and ricocheted to the left and back onto the field.

Umpires, apparently believing the ball had hit the top of the fence initially called the ball in play and Arroyo stopped at second, but after a video review he was awarded his sixth career home run.

"You've got to give Arroyo some credit," said Arizona manager Kirk Gibson. "He can swing the bat, he fouled several pitches off and he hit it out."

Skaggs (1-1), making his second career start, gave up three runs on five hits over 5 2/3 innings. He struck out five, walked two and hit a pair of batters.

"It felt good but I need to cut down on the walks, the walks and the hit batters," Skaggs said. "I think it would help my outing a little bit."

Justin Upton drove in both runs for the Diamondbacks, who have lost four straight and six of eight during their 10-game homestand.

Arizona slipped below the .500 mark for the first time since August 15 and trails San Francisco by 7 1-2 games in the NL West with 33 to play.

Arroyo (11-7) allowed two runs and five hits over six innings for his fourth straight win.

Sean Marshall came on in the seventh, Jonathan Broxton pitched the eighth and Aroldis Chapman retired the side in the ninth for his 32nd save.

Brandon Phillips added an RBI double for the Reds, who remained six games ahead of St. Louis in the NL Central and gave Baker his 400th win with the club.

Upton gave the Diamondbacks a 1-0 lead in the second with a solo home run to left. The Reds tied the game in the top of the third when Valdez singled and scored on Phillips' double to center.

After the unearned run gave the Reds a 2-1 lead in the fourth, Upton knotted the score in the bottom of the inning, singling home Aaron Hill with one out.

"With him (Arroyo), you just kind of have to get a pitch to hit and make sure he's on the plate," Upton said. "He works the corners a lot."

NOTES: Chapman has converted a franchise record 24 straight save chances. . Baker is the seventh manager in Reds' history to collect at least 400 wins. . Arroyo's last home run was June 17, 2010 against the Los Angeles Dodgers. ... Reds 1B Joey Votto, out with a left knee injury since July 17, did not work out with Class A Dayton because of inclement weather. He's expected to begin his rehabilitation assignment on Tuesday, weather permitting. ... RHP Johnny Cueto (16-6) will take the mound on Tuesday night for the Reds against Arizona rookie LHP Wade Miley (14-8). Cueto is tied with Washington's Gio Gonzalez and the New York Mets' R.A. Dickey for the NL lead in wins and leads the NL with a 2.47 ERA. With the trade of Joe Saunders to Baltimore, the 25-year-old Miley is the second-oldest pitcher in the Diamondbacks' starting rotation.