Making his third of the spring, Marcum allowed only one hit and didn't walk anyone in 3 2/3 innings Sunday as the Mets beat the St. Louis Cardinals 3-0.
Marcum and six relievers combined to give up just three hits.
"We pitched very well today," Mets manager Terry Collins said. "It starts with Shaun. Shaun made pitch after pitch and later in the game the relievers did, too."
Shane Robinson appeared to be fooled by an offering from Marcum in the second inning but still managed to stroke the lone hit off him, keeping the ball inside the left-field line.
"As far as mechanics and everything, which has been my main focus the last couple bullpens and today's start, everything felt a lot better," Marcum said.
St. Louis starter Jamie Garcia was equally baffling to New York hitters. The left-hander threw five shutout innings, surrendering four hits and a walk.
"I thought he threw the ball very well," St. Louis manager Mike Matheny said. "You could tell the ball was running all over the place. He had a real smooth, fluid action to him. I was happy to see the way the ball was coming out of his hand."
Marcum and Garcia impressed, but it was Trevor Rosenthal who put on the biggest show for the fans.
Rosenthal struck out the side in the seventh inning. It was his first game appearance since learning he was no longer part of the competition to become St. Louis' fifth starter, and that he would be concentrating on coming out of the bullpen.
Rosenthal generated a noticeable buzz from the crowd when four pitches reached 100 mph on the stadium radar gun.
"I wasn't trying to do anything too much extra right now -- just the same approach, trying to attack every hitter," Rosenthal said.
The performance reminded Matheny of the job Rosenthal did during the Cardinals' playoff run last fall.
"He's an absolute weapon to be used out of the `pen," Matheny said.
Jamie Hoffman hit a two-run double in the ninth.
LF Matt Holliday returned to the Cardinals' complex after missing a few days with a flu-like virus. Holliday did not play on Sunday, but Matheny said he will likely be back in the lineup in a couple of days. ... Following the game, Matheny planned to fly back to St. Louis and have surgery to repair a ruptured disk in his back. He expects to return to the dugout on Thursday. ... Matheny said 3B David Freese should be able to play the field on Monday, a week after injuring his tailbone while falling into the stands in an attempt to catch a foul ball. ... The Mets sent 10 players to minor league camp before the game, including top pitching prospect Zack Wheeler. ... Collins presented former New York Giants coach Bill Parcells a jersey with the letters "HOF" on the back that was signed by the team in honor of Parcells' selection to the NFL Hall of Fame. Parcells regularly attends Cardinals games during the spring.