In the last 20 seasons, 17 pitchers have lost more than 15 games while maintaining an ERA under 4.50.

Andrew Cashner could join that group Wednesday night at Petco Park. He's been more deserving of his defeats against the San Francisco Giants, who aren't yet conceding they have nothing to play for as Jake Peavy tries for his first win as a visitor in San Diego.

Though misfortunate, Cashner (6-15, 4.25 ERA) certainly hasn't had the year he or the Padres wanted. Yet he might feel like he has little room to complain compared to Shelby Miller, who is already there this season with 16 losses and a 3.00 ERA.

More from FoxSports

Cashner would be the second San Diego pitcher in as many seasons to join the group after Eric Stults went 8-17 with a 4.30 mark last year.

After limiting Arizona to three runs and seven hits in last Wednesday's 4-3 win, Cashner is coming off a rare victory, though he still has a 5.40 ERA and .409 opponent on-base percentage while going 1-3 in a five-start span.

His manager wants to see him simplify things and hopefully cut down on the 4.45 walks per nine innings he's posted in that time after having a 2.79 mark through 24 starts.

"Cashner was great; player of the game for me," Pat Murphy said. "He just attacked a very good offensive team ... with 75 percent (of his pitches) or more were fastballs. Hopefully, he learned something he can take with him going forward, that he doesn't need to go deep in counts. His fastball is that good."

The right-hander has lost both of his starts against San Francisco this season with nine earned runs allowed in 10 2-3 innings to fall to 2-3 with a 5.13 ERA in seven career starts in the series. Buster Posey (11 for 22 with two home runs) and Brandon Crawford (5 for 11 with a home run) have hit him best.

Cashner is up against Peavy, San Diego's former ace, who's again doing his part down the stretch. Peavy (7-6, 4.08) was 4-0 with a 1.15 ERA as the Giants won his last six regular-season starts last year.

The right-hander hasn't been quite as strong this time around, but after allowing two runs and seven hits in six innings of last Wednesday's 5-3 home win over Cincinnati, he's 4-0 with a 3.52 mark in his last five. He's also 7-0 with a 3.12 ERA in 12 September starts dating to 2013.

The 34-year-old has only faced the Padres (70-81) three times since leaving in 2009, going 1-1 with a 3.38 ERA and the loss coming in his only return to Petco on April 12. Justin Upton is 9 for 17 with two homers and a triple against him, but Yangervis Solarte is 0 for 8.

With Tuesday's 4-2 series-opening win, San Francisco (79-71) has won 10 of 15 and six straight in the series with a 47-10 scoring advantage. More importantly, it gained a game on the NL West-leading Los Angeles Dodgers, who have dropped four in a row.

The Giants remain six back with 12 to play, though four come at home against the Dodgers next week. Their other two remaining series come at Oakland and at home against Colorado, two clubs toiling in last place.

''We're still alive,'' manager Bruce Bochy said. ''I've talked about this so many times. You never know. You keep grinding, you keep fighting and see what happens. You've got to believe, and it's all up to us about winning games. That's where it starts. Of course, it's obvious we need a little help. There's a big series coming up.''

Posey (hip) was out of the lineup Tuesday but is expected back Wednesday.

Matt Kemp is batting .147 in his last nine games and .146 in his last 13 against the Giants.