PITTSBURGH -- The Pittsburgh Pirates and San Francisco Giants are looking like polar opposites as they get set to open a four-game series Monday at PNC Park.

The Pirates are plummeting.

Their 10-5 defeat Sunday against the Chicago Cubs was their fifth loss in a row and 10th in their past 11 games. They were a season-high nine games over .500 following a win in Texas on May 27. Since then, they are 5-17, leaving them three games under .500 (33-36).

The Giants (44-26), in sharp contrast, have it going on. They won their eighth game in a row Sunday, 5-1 at Tampa, moving them to 18 games over .500 and putting them on pace for a 101-win season.

It's San Francisco's second eight-game winning streak this season. Since May 11, the Giants are 27-8 (.771).

It's not because of power; their 59 homers rank among the bottom few in the majors.

It's not smoke and mirrors, either.

"We're just playing the way we play," pitcher Jake Peavy told the San Francisco Chronicle after Sunday's win. "This is the identity we talked about in spring training, who we are as ballplayers and who we are as a team. We just come out and play our best team game and have the best approach."

It's a balance.

"Just getting big hits, timely hits," manager Bruce Bochy told MLB.com. "It's been pitching keeping us in the game and giving us a chance. We're not scoring a lot of runs, but we're getting the timely hits when we need them, doing some little things right."

They haven't exactly been scoring a measly amount of runs. During the current win streak, they have scored 47 runs, 5.9 a game.

Pittsburgh would have to practically strike gold to match that run output Monday, as San Francisco is scheduled to start its ace, Madison Bumgarner (8-1, 1.91 ERA, 107 strikeouts, 26 walks).

He is 7-0 with a 1.27 ERA over his past 10 starts.

Pittsburgh pitching, like its hitting, has been erratic lately and the club is without No. 1 starter Gerrit Cole (triceps injury).

The Pirates will counter Monday with Jeff Locke (5-5, 5.92 ERA), who allowed seven runs in four-plus innings in his most recent start, an 11-2 loss Wednesday against the Mets. Locke has lost two starts in a row after winning four in a row.

Locke was 3-1 with a 3.98 ERA and a .203 batting average against in his six starts during May. He was feeling good enough about his game that he was working on a wrinkle -- adding a harder breaking pitch.

"More velocity with spin, (so) hitters start early," Pittsburgh manager Clint Hurdle said earlier this month. "Looks like a fastball leaving their hand, and then the late break. It would be nice for him to come up with something in between the fastballs and the changeup. He is working on it.

It's more of a slurve right now."

Locke does have one set of numbers in his favor.

He has been much better at PNC Park than on the road. At home, he is 3-1 with a 3.94 ERA and a .248 average against.