ST. LOUIS -- The Pirates lost, 4-1, to the Cardinals at Busch Stadium on Wednesday afternoon. The defeat ended the chance for a rare road series win, and it dropped the team's record away from PNC Park to a glaring 16-61.

However, of much more lasting significance was James McDonald's season-ending performance, which was further proof that he lines up to be a critical piece in the Pirates' future rotation.

As Pittsburgh looks ahead to 2011, McDonald has placed himself in position to be an integral part of the organization's pitching plans. He showcased that potential again on Wednesday, capping an 11-start stretch in which McDonald appears to have already made the Pirates winners in one of their three Trade Deadline deals.

"That drive he has, you can see it when he's on the mound," manager John Russell said. "When he's in the zone, he can be dominating. When he goes out there, he really is a competitor."

Coming off his most inefficient start since that trade, McDonald mostly breezed through his 80-pitch, six-inning effort. He allowed just one of the first 12 hitters he faced to reach and used two of his seven strikeouts to work out of a fifth-inning jam.

That efficiency, in particular, was the key, given that it hasn't always been McDonald's most favorable statistic. It was also a challenge in this start, as the Pirates had a strict eye on McDonald's workload because of how many innings he had already logged this year.

"I think he took the challenge and threw the ball really well," Russell said. "He really wanted to finish strong."

McDonald helped himself out by throwing a first-pitch strike to 15 of the 24 hitters he faced. His only costly mistake was a down-the-middle fastball to Allen Craig with two strikes and two outs in the fourth. Craig put the Cardinals ahead with a solo homer.

"He took a good at-bat," McDonald said. "I tip my cap to him. He took a good swing."

The score would be the same when McDonald's day ended. And with insufficient late-inning life from the Pirates' offense, McDonald ended up with his fifth loss of the season. His 4-5 record, however, is hardly indicative of the boost that McDonald has provided to the rotation.

He made his debut by striking out eight, immediately matching the team's high. He strung together 20 scoreless innings a few weeks later. He allowed more than three earned runs in only three of his starts.

And maybe as important as any individual statistic, McDonald was cited, more than once, for motivating the rest of the rotation simply through his own success.

Of general manager Neal Huntington's numerous trades, McDonald has made the swapping of 36-year-old reliever Octavio Dotel, which brought McDonald in return, look like one of the best. And while the Pirates aren't keen on handing over 2011 rotation spots at this stage, McDonald appears as near to a lock as anyone else on this staff.

"I'm a better pitcher, but there is still a lot of work to be done to be satisfied with what I did this year," McDonald said. "When next year comes, I have to compete, so I can still be a starting pitcher. I never have a peace of mind when it comes to competing. I really hate losing."

Pittsburgh's inability to keep McDonald from losing had something to do with Cardinals starter P.J. Walters, but more to do with a collectively unimpressive approach by the Pirates' hitters against him. Coming off a four-inning appearance last week in which the Pirates knocked him around for five runs and seven hits in four innings, Walters had the best results in his career.

Andrew McCutchen swung at Walters' first pitch of the game and reached on an infield single. From there, Walters sailed. He retired McCutchen on a double play and allowed no other Pittsburgh baserunner to reach through the first five innings.

The Pirates' only serious threat against him came in the sixth, which began with Ronny Cedeno's leadoff single. A two-out walk to McCutchen put a pair of runners on for Jose Tabata, but he couldn't capitalize and flew out to end the inning.

"We swung the bat terrible today," Russell said. "He made some good pitches, but we didn't do a very good job."

Russell was asked again if Walters had anything to do with that.

"We didn't have very good at-bats," Russell added. "That's the bottom line."

St. Louis saw things a bit differently.

"What didn't impress you?" Cardinals catcher Bryan Anderson said of Walters, who relied heavily on his fastball and changeup to get through the day. "His command of everything was perfect, and any time he's going to be like that, it's going to be hard for the other team to get hits and produce runs."

It wasn't until Walters had finished a career-long, seven-inning outing that the Pirates dented the scoreboard. McCutchen doubled and scored in the ninth to keep Pittsburgh from being shut out for the 15th time this year.

The Cardinals added an insurance run in the seventh with Aaron Miles' two-out RBI single off reliever Joe Martinez. Martinez allowed two singles, hit a batter and threw a wild pitch in the frame. Garrett Jones' throwing error opened the door for the Cardinals to score twice more in the eighth off Chan Ho Park.

With the loss, Pittsburgh missed a chance to collect just its fifth winning road series of the season. Instead, the Pirates head to Florida with just five second-half road victories.