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7/21/2013 3:00 P.M. ET

Padres 'pen remains rock solid, backs up rotation

ST. LOUIS -- After some much-needed rest during the All-Star break, the Padres' bullpen has gotten off to a strong start in the second half.

Aside from a three-run, two-inning outing from Sean O'Sullivan, making his first relief appearance since 2011, the 'pen limited a dangerous Cardinals offense to one hit and and two walks over 4 2/3 innings of relief.

"That's always been a strength of ours, the bullpen," Thatcher said. "We got worn out pretty good in the first half, and you know, we got a chance to get a couple days off. Everybody is fresh now, got a chance to step back and regroup a little bit."

Nick Vincent, Dale Thayer, Joe Thatcher and Huston Street combined to pitch four hitless innings Saturday night, with Street earning his 16th save.

"That's what our bullpen mostly does, is go out there and throw strikes and get outs," said Vincent, who has retired 14 of his last 16 batters. "When we get leads, our bullpen can come in and shut the door."

The Padres relievers are holding opponents to a .252 batting average and posted a 3.39 ERA heading into Sunday's series finale in St. Louis. The 'pen has been called upon often this season to pick up inconsistent starting pitching, making the four-day break last week all the more important.

"It's still going to be a long second half," Vincent said. "It just gets longer and longer as you get to the end. Games mean more every time."

Marquis placed on disabled list, Mikolas recalled

ST. LOUIS -- The Padres have placed Jason Marquis on the 15-day disabled list, retroactive to July 20, with a right elbow strain and recalled right-handed reliever Miles Mikolas from Triple-A Tucson.

Marquis sustained the injury in his Friday start against the Cardinals, in which he tossed 86 pitches over 5 1/3 innings. He was looked at by the Cardinals' doctor after the game and he will see Cincinnati-based doctor Tim Kremchek -- who performed a successful surgery to remove bone chips in Marquis' elbow -- for a second opinion.

Padres manager Bud Black said the issue didn't stem from a specific incident, as much as it was just cumulative throwing Friday. He said there is no timetable for Marquis to return, and he didn't rule out the right-hander missing more than 15 days.

"Where he is in his career, he knows that this is not a short-term thing," Black said. "He will be out. We don't know exactly how long or the extent of the injury. … I think when the MRI comes back, we can be more specific."

Marquis is 9-5 with a 4.05 ERA, but he hasn't earned a win since June 15, logging three no-decisions and three losses since. The latest was a 9-5 loss to St. Louis on Friday, in which he surrendered six earned runs on eight hits and three walks. He was unavailable postgame while he received treatment in the training room.

Mikolas is making his third stint with the Padres this year. Black said early Sunday afternoon that Mikolas was en route from Tucson to St. Louis and was available in relief after arriving during the early part of the 1:15 p.m. CT game.

The 24-year-old righty was recalled by San Diego on July 9 and made one relief appearance two days later, pitching a scoreless ninth against the Giants before he was optioned back to Tucson the next day. Mikolas, a seventh-round selection of the Padres in the 2009 Draft, was also recalled in late June, but he did not pitch in any games.

Ross back in rotation, set to start on Tuesday

ST. LOUIS -- Manager Bud Black announced Sunday that Tyson Ross will return to the Padres rotation, getting the start Tuesday in Milwaukee.

Ross began the season as the fifth starter and went 0-1 with a 3.86 ERA in three starts before he was placed on the disabled list with an impingement in his left shoulder on April 20. He came off the DL on May 5, and though the injury to his non-throwing arm didn't affect his pitching, he wasn't healthy enough to swing a bat, bumping Ross into the bullpen as a long reliever.

He was sent down to Triple-A Tucson earlier this month to stretch back out into a starter. He made two starts in Tucson, pitching five scoreless innings July 12 and, most recently, tossing 78 pitches over 4 2/3 innings Thursday.

"We feel as through now, he's ready both physically and with pitch count," Black said. "We think that the injury earlier in the year has been resolved, the strength is back in the left shoulder. He's able to swing. We feel good about that."

But just as soon as Tuesday's rotation spot was filled, another opened up. With Jason Marquis headed to the disabled list, Wednesday's start in Milwaukee is now up for grabs. Black said Sunday that he will announce the starter sometime in the next few days, as soon as he informs the player first. The open Wednesday spot is just the latest in a long line of rotation shuffles for San Diego, which has sent nine different starters to the mound this year.

"It's not ideal," Black said. "It's been unfortunate, there's no doubt. Any team will tell you from the front office down to the clubhouse, the best scenario is to have your five guys out of Spring Training and have those guys ... make their 33, 34 starts.

"What we've had to go through the last couple of years is obviously not that. Whether it's veteran guys coming in or youth from our Minor Leagues, but that's what we've got. And we're going to make the most of it."

Chad Thornburg is an associate reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.