CHICAGO -- It was not that long after manager Ozzie Guillen finished saying that starting pitching was the key to his team's chances that Jose Contreras was writhing on the ground with a ruptured left Achilles' tendon.

The Chicago White Sox were supposed to be breathing a sigh of relief with Contreras back on the mound for the first time since July 13 after a bout of right elbow tendinitis.

That sense of well-being lasted just 1 2/3 innings on Saturday night. That was when Contreras was injured while rushing over to cover first base on a ball hit wide of the bag by Jacoby Ellsbury, the fastest man on the Boston Red Sox. Contreras fell as the toss to first came from Nick Swisher and Ellsbury beat the play.

Contreras rolled on the ground in obvious pain, pounding his fist on the ground, before eventually leaving the field and the game. For Contreras, 36, the season is over. He won't pitch again, if he pitches again, until the second half of the 2009 season. The question now is what the White Sox can do with the remainder of the season without one of their starting five.

"It's a sad day," Guillen said after Saturday night's game. And that sadness was bigger than a 6-2 loss to the Red Sox or even falling into second place in the American League Central behind the Twins.

Just before the game, Guillen had been asked what he was looking for from Contreras in his first start coming back from the disabled list. The manager smiled and responded: "Give me eight [innings], please."

Chicago could use more innings from its starters to give a break to a heavily worked bullpen. Guillen's fondest dream might have been for eight innings from Contreras, but he probably would have happily settled for six. But 1 2/3 innings, with a serious injury, was a nightmare scenario.

The White Sox have had sturdy pitching for most of the season. They couldn't have spent 108 days in first place without it. But over the past month, they have suffered through a pitching slump, posting a team ERA of 6.04 over 23 games, the highest mark in the Majors during that period.

Thus, many of Guillen's remarks this week, during the earlier series against Detroit and the current one against Boston, have been about the absolute necessity for his pitchers, particularly his starters, to lift their level of performance. The return of Contreras seemed to offer an opportunity for that to occur in a natural way. Instead, it merely opened up the door for a truly disappointing development.

The White Sox are no different than anybody else when it comes to relying on pitching over the long haul. But their recent struggles on the mound have underscored the importance of pitching, particularly to a club with legitimate postseason aspirations, a club locked in a tight race with the Twins for a divisional championship.

The White Sox starting pitching has been a bit on the unexpected side, anyway, because the most consistent performers in the rotation have been, by the numbers, the two youngest and least experienced starters, Gavin Floyd and John Danks.

Mark Buehrle has been more erratic than the Sox would have liked, although he showed what he was capable of on Friday night, completely stifling the difficult Boston lineup. Javier Vazquez has been roughly in the same category. The fact that the White Sox have been this successful with Buehrle and Vazquez a combined 17-20 is a tribute to the work of Floyd and Danks and the strength of the rest of the team.

Exacerbating the pitching problems is the fact that reliever Scott Linebrink has been on the disabled list since July 26 with right shoulder inflammation. Linebrink had been the Sox most dependable setup man, or, as Guillen put it: "When we had Linebrink in the eighth and [closer] Bobby Jenks in the ninth, I was a genius."

In his pregame session with the media, responding to questions on individual pitchers, Guillen had stressed that from this point on this season, expectations were going to increase for everybody in the starting rotation.

"It's everyone, it's all five guys," the manager said. "We're going to score runs. It's our starting rotation that's going to determine how we play."

That whole concept took an obvious hit with the injury to Contreras. But the question of what to do next in the rotation may have answered itself in this same game. Reliever D.J. Carrasco turned in a sturdy performance in relief of Contreras, pitching 4 1/3 innings and giving up just one run. Carrasco has been a reliever for most of his career, but he made 20 starts with the Kansas City Royals in 2005.

"Now we might start Carrasco," Guillen said. "I'm not 100 percent set, but in my heart, I think he might be the guy."

Left-hander Clayton Richard, who had an opportunity in Contreras' absence, did not appear to be the answer. In three starts, he never got out of the fifth inning and had a 10.38 ERA.

"I don't think he threw the ball good enough to be up here, to be honest with you," Guillen said of Richard.

The White Sox also gave themselves another potential option when they obtained left-hander Horacio Ramirez in a trade with Kansas City after the game on Saturday. Ramirez has been a reliever this season, but he has made 104 big league starts.

It could be argued that Contreras (7-6, 4.54 ERA) was three seasons beyond his best work, but he had pitched effectively earlier this season. At the very least, the White Sox could have reasonably hoped that he could eat some innings and pitch competitively. Now they will have to get the innings elsewhere.

For the White Sox, the return of Contreras held out the hope of at least some additional rotation stability. Instead, this event turned into a major injury, at the worst possible time, at the most critical position.

Guillen said he expected that each of the four remaining starters would "step it up a notch." That seems more like a necessity than a hope at this point.