SAN FRANCISCO -- Round 1 goes to the Giants.

In the first of three games between the surprising first-place and second-place teams in the NL West, the Giants roughed up Arizona right-hander Zach Davies and put up a five-run fifth to beat the D-backs, 8-5, on Friday night at Oracle Park.

With the loss, the D-backs' lead dropped to 2 1/2 games over the second-place Giants and three over the third-place Dodgers.

The D-backs came into the game having won nine of their last 10 road games and 12 of 14 while the Giants were winners in 10 of their previous 11 games.

“They played a good game and we didn't,” D-backs manager Torey Lovullo said. “We played several good innings but at some crucial moments, we just didn’t execute. The fifth inning was the separator.”

The Giants had a 3-2 lead heading into the fifth when the D-backs scored a pair of runs to go up by one. It seemed like it was setting up to be another game in which the D-backs would trail early but manage to do just enough to come back and win.

But in the bottom half of the fifth, Davies walked the leadoff hitter, and things went downhill from there.

Joc Pederson reached on an infield single and J.D. Davis followed with an RBI double to chase Davies from the game.

Reliever Joe Mantiply then hung a slider to Michael Conforto for a two-run double and Mantiply missed his spot with a sinker to Patrick Bailey, who sent one into the seats in left-center for a two-run homer.

It was the third straight poor start for Davies, who has allowed 18 earned runs over 10 2/3 innings over that stretch.

“I tried to make some changes between starts and tried to go back to how I felt in years past,” Davies said. “You know, a couple of innings there I felt pretty good with it and then other ones got away from me and then a couple of big innings bit me again.”

Davies is an important member of the Arizona rotation. Zac Gallen and Merrill Kelly provide a formidable one-two punch at the beginning of it, and the team is counting on Davies to provide stability and innings in the middle of it ahead of youngsters Tommy Henry and Ryne Nelson.

In two starts prior to this last stretch for Davies, he had allowed five earned runs over 12 1/3 innings.

“He's a big piece of this rotation,” Lovullo said. “I felt like Zach’s stuff was better tonight than it was the previous two and it's just about moving forward and taking steps in the right direction. So I thought there was progress, but I just feel like there were a couple moments that we all need to be better at.”

Davies spent last year pitching for a struggling D-backs team. This year, though, it’s been a different story with Arizona being one of the surprise teams in the NL. That makes his struggles all the more frustrating for Davies.

“It's a great group of guys and you want to contribute,” Davies said. “The team, the players, the coaching staff, it's all great and you don't want to feel like you're the guy lagging behind. You’re not trying to make a competition with other players but you want to feel like you're pulling your weight. It's probably the toughest three-game stretch of my career. I've had tough stretches in the past, but you believe in yourself and you trust yourself and you come out of it.”

Davies will have to wait another five days to redeem himself, but the D-backs have a quick turnaround for a day game Saturday. Friday night’s game had a buzz to it with a pair of hot teams facing each other, and the D-backs would have liked to have shown out better.

“We deserve to play in these situations,” Lovullo said. “We’ve earned it. It‘s just unfortunate that we didn't play our best game. I think they played a very good game and we didn’t. We’ve got to turn it around tomorrow.”