SAN DIEGO -- TBA has become a regular in the Padres rotation this season.

Three-fifths of the rotation the Padres had on Opening Day are gone.

Actually, the projected top three pieces of the rotation are currently missing.

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Andrew Cashner joined Tyson Ross, who hasn't pitched since Opening Day, on the disabled list Saturday. And James Shields has been traded to the Chicago White Sox.

When the season opened, Ross was the Padres' No. 1 starter followed by Shields and Cashner, with right-hander Colin Rea in the No. 4 slot and left-hander Drew Pomeranz the No. 5 starter.

Sixty-four games later, Pomeranz is the ace of the staff and Rea, who faces the Miami Marlins and left-handed starter Wei-Yin Chen Monday night in the opener of a three-game series at Petco Park, has been the second-most active Padres starter.

"It's been tough," Padres manager Andy Green said Sunday when he talked about the state of his rotation. "But it's the hand we've been dealt. It's been less than ideal, but we have to play it the best we can."

Pomeranz, who starts the second game of the series against Miami Tuesday night, is the only member of the Padres rotation who has made every start this season. Rea missed one when the Padres optioned him to Triple-A El Paso on May 23 as a way to control his innings.

But Rea was rushed back to San Diego after Cesar Vargas went on the disabled list. Then Shields was traded and ... well, the Padres have already used 10 starting pitchers this season, including 23-year-old Rule 5 draftee Luis Perdomo, who is the Padres' No. 5 starter until Cashner returns from his neck strain.

The plan to rest Rea and control the 25-year-old's innings has temporarily been scrubbed.

He will be making his 12th start of the season Monday (7:10 p.m.) while facing the Marlins for the first time in his career. Ironically, Wei, who will be making his 130th career start, has never faced the Padres.

And this will be the first meeting of the season between the two teams, each of which lost the rubber games of series on the road Sunday.

Miami was blanked 6-0 by Arizona in Phoenix as it fell to 2-4 after two stops of a three-city road trip.

The Padres dropped a 2-1 decision at Colorado ... adding to one of the worst stats in all of baseball for 2016. The Padres are 0-10 on Sundays this season -- and 1-20 in the finales of the 21 series they've played to date.

On the flip side, the Padres are 14-7 in the openers of series.

Rea is 3-2 with a 4.74 earned run average going into his 12th start of the season. Chen is 3-2 with a career-high 4.56 ERA going into his 13th start. Chen, a product of Taiwan by way of the American League, has only one win in his past seven starts. Rea is 0-1 in his last five starts.

One area where Rea might have an edge is with the bat. Rea is 3-for-22 this season with an RBI and three runs scored and is 5-for-31 in his career. Chen is 0-for-28 in his career at the plate and recently switched to hitting right-handed.

"I just started hitting right-handed," Chen recently told Miami reporters, "so I'm going to need a little time adjusting."

Chen's first hit wouldn't be the first hitting milestone for a pitcher against the Padres this season. Bartolo Colon hit the first homer of his career against Shields when he was still with the Padres on May 7.