SAN FRANCISCO -- Two pitchers making important starts at opposite ends of the career spectrum lock horns Saturday when the Washington Nationals duel the San Francisco Giants.

In the third game of a four-day series between National League division leaders, each team will be counting upon a pitcher who has done little or nothing to help get his team to the top of the pack.

For the second time this season, the Nationals are recalling right-hander Reynaldo Lopez from Triple-A Syracuse to start against a playoff contender.

The first time did not go well. The 22-year-old was roughed up for 10 hits and six runs in 4 2/3 innings at home against the Los Angeles Dodgers earlier this month.

Lopez was impressive in one regard in his debut. He struck out nine Dodgers among the 14 he retired.

Nationals manager Dusty Baker announced Friday he'd be pairing Lopez with someone with whom he's quite familiar. Pedro Severino, summoned from Syracuse to San Francisco one day ahead of Lopez, will catch the game, Baker disclosed.

Washington will be trying to build upon the momentum of two wins to open the four-game series. A triple play, the first in Nationals history, helped save Friday's 4-1 win.

"That's the first triple play that I've seen," insisted Baker, who has 39 years of experience as a major league player and manager. "There have been others. But I always seemed to be in the bathroom when it happened."

The Nationals have received brilliant pitching performances from right-handers Tanner Roark and Max Scherzer in the first two games of the series, only to have to sweat out exciting finishes once their fate got turned over to the bullpen.

Two days ahead of the trade deadline, the Giants will send righty Jake Peavy to the mound to oppose Lopez.

The 35-year-old Peavy will be making his 14th career start against the Nationals, the first having come 14 years ago when the club was known as the Montreal Expos.

Peavy has won 152 games in his career, but only five in 20 starts this season.

That lack of production, coupled with fellow veteran Matt Cain's two-win season, has the Giants reportedly active in trade discussions for a starting pitcher at the deadline.

It's possible Peavy or Cain, who will face the Nationals on Sunday, could lose his job with one more poor effort.

San Francisco manager Bruce Bochy insisted Friday he's more concerned about turning around the club's recent woes -- the Giants are a worst-in-baseball 2-11 since the All-Star break -- than pondering trades or changes in his starting rotation.

"It kind of is, really, when you get in these funks, what can go wrong, goes wrong," he lamented. "When you're in a good winning streak, the ball bounces your way. Everything's your way. And right now it's not going our way."

The Giants are expected to have Hunter Pence back in the lineup for Game 3 of the series.

Pence has missed 48 games with a strained right hamstring.