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SAN DIEGO -- During Tuesday night's 70-minute rain delay at Petco Park, some fans wondered why the Padres and Arizona Diamondbacks were working so hard to get the game played.

Well, for one, neither team really wanted to play a doubleheader on Wednesday's get-away day.

Secondly, the worst teams in the National League West are in a head-to-head struggle for prime position in next June's amateur draft.

Going into Wednesday night's series finale at Petco Park, the Padres are sitting in the No. 4 slot following two straight wins over the Diamondbacks to escape the National League West basement. And Arizona is now tied for the third-worst record in the major leagues.

While both the Padres and Diamondbacks would benefit more by losing at this point in terrible seasons, each team is playing something of their aces Wednesday night.

Well, the Diamondbacks are certainly playing their ace. Right-hander Zack Greinke is 12-6 with a 4.54 ERA. And, during the course of his National League career, Greinke has been tough on the Padres -- with the exception of that 2013 scrap with Carlos Quentin that landed Greinke on the disabled list with a broken collarbone.

Greinke is 7-1 against the Padres in 15 starts, with a 1.96 ERA and a .189 opponent batting average. He is 1-0 with a 3.54 ERA in three starts against the Padres this season.

Over his last two starts, Greinke has a 3.00 ERA, having allowed four earned runs in 12 innings. And he's far from satisfied.

"I felt pretty good, but not perfect," Greinke said. "I've just been missing by a little bit on just about every pitch. I've not been able to put a whole start together of good pitches. I'm getting behind and trying to make a good pitch, and just missing by little bit again."

The Padres' starter is not an ace, but the Padres are beginning to believe that 23-year-old Rule 5 pick Luis Perdomo has the pitches and mindset to develop into this one.

Padres manager Andy Green calls the development of Perdomo as a starting pitcher one of the biggest plusses of the season. Pitching coach Darren Balsley says Perdomo, who a year ago at this time had finished a season at low Class A, is not satisfied just to reach the majors.

"He is absolutely driven to be the best pitcher he can possibly be," Balsley said recently. "He's not happy with the strides he has made this season -- and they have been huge. He wants to be something special."

Perdomo has been over his last five starts. During the run, he has allowed 11 runs on 32 hits and five walks, with 22 strikeouts, in 35 innings. Perdomo is 3-2 with a 2.83 ERA during the run and has the only complete game pitched by a Padre this season.

Overall, Perdomo is 8-9 with a 5.68 ERA in 18 starts. His ERA has fallen in 12 of his last 14 starts.