CINCINNATI -- Derek Norris admitted to losing some confidence in mid-May when his batting average bottomed out at .167.

"The back half of May I was swinging the bat pretty well," Norris said. "I just stuck with the process."

But, the old adage is that it's a long season, and Norris' resolve is beginning to pay off.

On Thursday night, Norris hit a three-run home run and Matt Kemp added a solo shot, lifting the San Diego Padres to a 7-4 victory over the Cincinnati Reds in the opener of a four-game series at Great American Ball Park.

The Padres trailed 4-3 in the seventh before Norris connected for his three-run shot off J.C. Ramirez to put them ahead to stay.

"We counted on him to be a middle of the order production guy," said manager Andy Green. "It's good to see him get going. There was no point in time we thought he was going to hit .160."

It was the 54th home run allowed by the Reds' bullpen this season, and Norris' third in five games. He's now hit safely in 13 of 17 games in June.

"A homer here and there, sure," Norris said. "Definitely some work still left to do. I felt there were some more pitches to hit tonight that I fouled off. I'll keep improving."

Melvin Upton Jr. went 2-for-4 and scored twice for San Diego (31-43). The Padres improved to 13-21 on the road this season.

Both starting pitchers fell victim to elevated pitch counts.

Reds right-hander John Lamb failed to pitch past the sixth inning for the sixth time in nine starts, allowing four earned runs over 102 pitches in 5 1/3 innings.

"I just need to get outs," said Lamb. "I can't sum it up any other way. I need to make good pitches and get outs. It's a matter of just continuing to bear down. Every pitch is an important pitch."

Padres right-hander Christian Friedrich (4-2) couldn't recover from a lengthy third inning, and he tossed 101 pitches and gave up four runs over five innings. However, the bullpen shut the door on the Reds' offense to earn him a victory.

"He lost glove-side command of the fastball," Green said. "Those (long) innings were tough on him. He couldn't find that one pitch."

Fernando Rodney, who allowed his first earned run this season in his previous outing, pitched the ninth for his 16th save.

Travis Jankowski, starting in place of the injured Jon Jay, provided some insurance for the Padres with an RBI single in the ninth inning. He drove home Adam Rosales, who had doubled.

Ramirez (1-3) took the loss after yielding two runs in two-thirds of an inning.

Cincinnati (28-45) hasn't won a season series against San Diego since 2012 and is 6-13 against the Padres since then.

Friedrich needed 39 pitches to get through the second inning and escape a bases-loaded jam. He wasn't as fortunate in the next inning.

Cincinnati began the third with three straight hits, including consecutive doubles by Zack Cozart and Billy Hamilton and an RBI single by Brandon Phillips.

Adam Duvall's 21st homer, a two-run shot, made it 4-1. He leads all major league left fielders in homers. All four runs and four of the six hits allowed by Friedrich came in the third.

"I started rushing from one pitch to the next," Friedrich said. "I left that pitch to Duvall up. It's nice knowing (the bullpen) can come in behind me and do the job."

San Diego got a run back in the fourth when Kemp led off with his 16th home run. Yangervis Solarte's RBI single in the sixth sliced the deficit to 4-3, and Solarte and Upton scored on Norris' homer.

"Home runs that give up the lead or extend the lead are tough," said Price. "That's been somewhat of a nemesis this year. I'll take that back. It's been a huge nemesis this year."

NOTES: Reds 1B Joey Votto again was out of the lineup Thursday after missing two straight games due to a stomach virus. He struck out as a pinch hitter in the ninth. ... Reds RHP Homer Bailey, who hasn't pitched since April 2015 after elbow surgery, will begin a rehabilitation assignment Monday at Triple-A Louisville. He's expected to make up to five rehab appearances to get stretched out to 90-100 pitches. ... Padres CF Jon Jay was out of the lineup. He's day to day after being hit by a pitch on Sunday. Travis Jankowski started in center.