He can't be now.
In what was expected to be his final start in the rotation, Karstens made an exceptionally strong case that he should not be the one bumped out when Ross Ohlendorf returns. His six scoreless innings on Saturday carried the Pirates to a 2-0 win in front of 25,047 at PNC Park.
The victory surely erased the bitter taste of Friday's fundamentally faulty loss. It will also force management to potentially rethink its rotation options, even if that was not Karstens' sole motivation going into the night.
"I'm not really worried about that," Karstens said of the soon-to-be-crowded rotation. "I'm just worried about giving us a chance to win."
But still, after weeks of begging for starters to step up and seize rotation spots, the Pirates now find themselves with one too many. Two days ago -- after Brian Burres posted his second straight scoreless start -- the decision seemed easy. Based on merit, Burres would remain with the big league club. Based on numbers, Karstens would be the one giving his rotation spot to Ohlendorf.
Well, things don't look so clear cut now.
"Good problems to have," manager John Russell said afterward, not yet tipping his hand as to what Karstens' immediate future may hold. "That's what he's capable of doing. He seems to rise to the occasion when it's a big game."
Looking even better than he did when he stepped up big in Milwaukee on the last road trip, Karstens rolled through what was his third start with the club. There was masterful efficiency -- Karstens threw just 74 pitches -- and particularly tremendous use of his sinker.
The right-hander breezed through the first five innings, allowing just one walk and one double.
"I can't say enough about him," catcher Jason Jaramillo said. "He got out of whack a few times, but he caught himself. That's the biggest thing. He was fun to catch."
Karstens did this, too, coming off a forgettable outing to the Dodgers in which he gave up six runs on 11 hits in five innings.
The only real trouble Karstens got into brewed in the sixth, and home-plate umpire Marty Foster helped him out of it. Foster's aid came late in the inning when, with Ryan Ludwick on second and Albert Pujols on first, Karstens served up a line-drive single to left.
Lastings Milledge came up throwing as Ludwick was waved home. Jaramillo took the throw, which was well up the line in foul territory, and tried to make a backhanded swipe as Ludwick passed him.
Foster ruled Ludwick out, buying Jaramillo's sell of the tag.
"The throw just took me up the line, and I tried to make the tag as soon as possible," Jaramillo said. "It worked out for us."
Yes, but did he really tag Ludwick?
"He called him out," Jaramillo promptly answered.
Ludwick and Cardinals manager Tony La Russa voiced their disagreement to Foster, and replays showed that they had good reason to. Jaramillo never applied the tag.
"You don't ever see me get that upset unless I know for a fact that I was safe, and obviously I was safe," Ludwick said. "I guess he didn't have a great angle. I knew I was safe."
La Russa added: "When you play nine innings, you are certainly not going to blame whatever that call turned out to be. That certainly didn't beat us."
No, the Pirates' pitching did.
That would be Karstens' final inning, as he left with the Pirates clinging to a 1-0 lead, which was the product of three consecutive singles by Steve Pearce, Jaramillo and Ronny Cedeno in the second. And from there, the bullpen was lights out.
D.J. Carrasco and Jack Taschner combined to pitch a scoreless seventh. Octavio Dotel recorded his sixth save with a scoreless ninth. In between, Joel Hanrahan took down Pujols in the most intriguing matchup of the night.
After allowing an infield single and hitting Ludwick in the hand, Hanrahan had no choice but to face Pujols -- a lifetime .369 hitter at PNC Park entering the game -- with the tying run on second.
"Not really the way you want to draw it up," Russell said.
After working the count to 1-1, Hanrahan got a called strike on a fastball at Pujols' knees.
"I did a no-look pitch," Hanrahan said, referring to the fact that he never looked back either runner. "I think I might have messed up his timing a little bit."
He then came back with a slider, and Pujols swung right through to end the inning. Hanrahan came off the mound visibly pumped up.
"I just threw a slider as hard as I could and made sure it wasn't close to the plate," Hanrahan said. "I don't show a lot of emotion out there usually, but that's kind of a big situation, so I let it out a little bit."
Jaramillo then provided a critical insurance run in the bottom half of the inning with a two-out single up the middle.
"To get that big hit for us late was kind of the icing on the cake for him," Russell said. "He did a tremendous job for us tonight."
The win was the Pirates' fourth in five games, all of which have had a common theme. Pittsburgh starters have now pitched six innings in each of those games after going that deep into a start just 10 times in the first 25.
Such consistency has obviously done wonders for the bullpen as well, which has combined to allow just two earned runs in 13 1/3 innings during this homestand.
Jenifer Langosch is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.