There was a 69-minute rain delay in the top of the sixth inning with two outs, following an RBI double by Alexi Amarista.
The Padres (28-28) took advantage of early scoring opportunities, taking a 4-0 lead after the third inning. Ross (3-5) finished with seven strikeouts and allowed five hits with three walks. He's 4-0 with a 1.16 ERA in five career appearances, including four starts, against the Reds.
Jon Moscot made his Major League debut for the Reds (23-30), replacing scheduled starter Raisel Iglesias. Moscot (0-1) struggled in his first three innings before retiring the final seven batters he faced. He finished the game with four earned runs on four hits and three walks and three strikeouts.
"He's a southern California kid, he's very familiar with those players over there with San Diego, but of course he's only seen them on TV, and now he's playing against them," Reds manager Bryan Price said. "So I thought he really managed the game after that first inning. He gave up a couple of other runs, one in the second, one in the third after two in the first, but he had much better command."
Reds second baseman Brandon Phillips made two sparkling defensive plays. The first came in the seventh inning when he snagged a grounder hit by Venable by ranging far to his left and flipping it to pitcher Pedro Villarreal, who was running to cover first base, just in time to beat the runner.
Then in the eighth, Phillips robbed Middlebrooks of a hit and started a double play. Middlebrooks hit a sharp grounder up the middle, and Phillips was able to slide in time to get his glove on the ball and quickly convert an around-the-back toss to Zack Cozart for the first leg of the 4-6-3 double play.
MOMENTS THAT MATTERED Getting RISPy with it: Middlebrooks continues to come up big for the Padres in terms of driving in runs. On Friday, he had a sacrifice fly in the first inning and then, two innings later, hit a home run to center field. He now has 12 RBIs in the last nine games. More >
Rough welcome to Majors: Moscot started the game with a strikeout of Venable, but it went downhill quickly for the right-hander in his Major League debut. Moscot gave up runs in each of the first three innings, including solo home runs by Venable and Middlebrooks in the second and third innings. The rookie did finish strong, retiring 11 of the last 12 he faced, including the final seven in a row. More >
"Obviously, as a starting pitcher you want to go as deep into the ball game as you can and the fact that I didn't get to go six innings is something that I am not happy with myself about," Moscot said.
Bearing down: Having already yielded a two-run single to Votto in the fifth inning, and with two runners on, Ross struck out Todd Frazier and then caught Jay Bruce looking at a called third strike to avoid any further trouble to end the fifth. Ross finished with seven strikeouts.
"The last few pitches at the end [of the fifth] were very good. Overall, his stuff was good. The slider was a little better than it was the last couple of outings," Black said of Ross.
Votto provides only scoring for Reds: With the bases loaded and one out in the bottom of the fifth, Joey Votto knocked in a pair of runs with a single to left field. The single by Votto cut the Padres' lead in half, and gave him his fourth multi-RBI game in his last six appearances.
"That's just as exciting as homers," -- Ross, on fine defensive catches in the outfield by Matt Kemp in right field in the third inning on a sinking line drive by Frazier in the third inning and then Venable's diving catch in center field on Billy Hamilton's line drive in the seventh inning
SOUND SMART WITH YOUR FRIENDS
It was another fast start for the Padres, who scored two runs in the first inning off Moscot. Runs in the first inning aren't unusual for this team. In fact, the Padres lead the National League in first-inning runs (42) this season.
BACK TO .500
With the victory Friday, the Padres climbed back to .500 for the first time since May 19 when they defeated the Cubs, 4-3.
WHAT'S NEXT Padres:Andrew Cashner gets the start in the second game of the series at 1:10 p.m. PT, coming off a start that he called "weird," where he struck out 12, allowed 11 hits and five earned runs in 4 2/3 innings against the Mets.
Reds:Michael Lorenzen will take the mound for the Reds in the second of a three-game series against the Padres at 4:10 p.m. ET. The rookie right-hander was up and down in his last start, giving up only two earned runs on one hit, but walking six in 6 1/3 innings of work against the Nationals on May 31.
Corey Brock is a reporter for MLB.com. Keep track of @FollowThePadres on Twitter and listen to his podcast. Robert Bondy is an associate reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.