Marcum became the first pitcher to last fewer than five innings in each of his first three starts with the Mets.
"I think that Shaun tried to hurry through his rehab and tried to get up here because he knew we needed help," manager Terry Collins said. "We've just got to run him out there again."
For a time, it seemed as if Marcum might not even make it as long as he did. The Pirates began shooting balls all over Citi Field in the second inning, beginning with Garrett Jones' double, Jose Tabata's hit and an RBI knock from Pedro Alvarez.
After Michael McKenry's double, pitcher Wandy Rodriguez smacked a run-scoring line drive off Marcum's non-pitching wrist, prompting multiple trips to the mound from trainer Ray Ramirez and ultimately an X-ray, which was negative. But Marcum stayed in the game, inducing a ground ball that Ruben Tejada double-clutched while throwing to first. Starling Marte beat Tejada's delayed throw, allowing a third run to score as the Pirates batted around in the inning.
"I feel good," Marcum said. "The thing is, I'm just not making pitches. When you don't throw 95, the balls up in the zone are going to get hit. The main thing I've got to get back to is locating the ball down in the zone."
Marcum did that for a time, retiring seven in a row before abruptly ending that streak on a leadoff hit batsman in the fifth. Jordy Mercer followed with a single, and Jones hit a replay-reviewed, three-run homer off the right-field wall.
The final damage against Marcum was six runs on nine hits over 4 2/3 innings. His fastest pitch of the evening came in at 87 miles per hour; mostly, Marcum sat in the low- to mid-80s.
"He was out there battling, giving it everything he had," catcher Anthony Recker said. "A couple pitches just missed a couple spots, and we weren't really on the same page."
It did not help that the Mets finished 0-for-9 with runners in scoring position against Rodriguez, touching the lefty for one run in six innings. That came on Recker's leadoff homer in the fifth, one of three leadoff hits the Mets accrued. David Wright provided the other two, but found himself stranded in scoring position each time.
"It's weird how things seem to equal out," Wright said, referencing his team's hot start to the season. "It seems like we have one or two opportunities a game to score runs, and if we don't do it then, then we don't do it."
Significant offense did not come for the Mets until the ninth inning, when Jordany Valdespin homered and Andrew Brown singled in another run. But it was far too little, far too late for the Mets, thanks in large part to Marcum's early struggles.
Well aware of the right-hander's injury history when they signed him to a one-year deal this winter, the Mets loaded Marcum's contract with incentives based on innings pitched and days spent on the disabled list. But they still guaranteed him $4 million, believing he could replace a significant chunk of the innings that R.A. Dickey took with him to Toronto.
That vision clouded midway through Spring Training, when Marcum began missing time with an injury that evolved from an impingement in his right shoulder, to nerve inflammation in his neck, to right biceps tendinitis. No matter the ailment, the Mets were glad to have Marcum back when he finally made his Mets debut in the final days of April.
Then he went out and gave up 18 runs over his first three starts, lasting a total of 13 innings in those outings. Marcum's season ERA, which includes an extra-inning relief appearance last week in Miami, is up to 8.59.
"Usually when I get hit pretty hard, it's because I'm missing location," Marcum said. "It's just a matter of going out and doing it in a game."