On Tuesday, in another difficult outing, Perez submitted six more walks, and one hit batsman, putting runners onto the basepaths for the Nationals to drive home.
The Nationals tallied four runs in six innings off Perez in the 4-0 Mets loss. Three of those scores initially reached by simply watching Perez hurl four balls past them.
"Oliver has been battling that his whole career," third baseman David Wright said. "When he's throwing strikes he has some of the best stuff for a left-hander in the game. When he doesn't throw strikes, the opposing team can take away certain pitches and sit on a pitch.
"He shoots himself in the foot sometimes."
It's not as if a controlled outing from Perez would have done the Mets any better. They were shut out for the fifth time in 13 games -- this time by Washington ace John Lannan. It was the first complete-game shutout by a Nationals pitcher since Pedro Astacio on Aug. 15, 2006.
"Very staggering stats by today's standards," Mets manager Jerry Manuel said, referring to the frequency of his team being shut out recently. "You see teams scoring runs, and we seem to be saving ours for the next day."
Lannan, who hits 90 with his fastball on a good day, only struck out one Mets batter. But he kept hitters off balance, induced 17 ground-ball outs and gave Perez a lesson in accuracy, tossing 80 of 106 pitches for strikes. He walked no one.
"A lot can be learned by watching him pitch as a young pitcher, or a big league pitcher," Wright said.
At Nationals Park on June 6, Lannan suppressed the Mets in similar fashion, holding them to an unearned run in a four-hit complete game.
On Tuesday, he used his patented sinker to scatter seven singles, only once allowing a runner to reach second base.
"He's been very tough on us this year," Manuel said. "He has our number at this point."
The Nationals began the game's scoring unconventionally in the bottom of the fourth, but not before Perez issued a pair of walks to set it up. With the bases loaded, Alberto Gonzalez hit a tailing line drive to Jeff Francoeur, who dropped the ball, but gathered it and fired to second base for a forceout, as Ryan Zimmerman trotted in to score from third.
Francoeur said his mistake may have altered the game's momentum, but the play ultimately had little effect. The next batter, catcher Wil Nieves, punched a base hit to the opposite field that plated Adam Dunn.
In the fifth, Perez drilled leadoff batter Nyjer Morgan with a 3-2 pitch and then walked Zimmerman two batters later. The two Nats baserunners scored on Dunn's single and Josh Willingham's sacrifice fly, respectively.
When asked about his control problems, Perez responded, "Right now, the more important thing is to get the win."
The Mets (44-49) have lost 15 of the past 22 contests. They will have to win on Wednesday to prevent a series loss to the Nationals (27-66).
Only one true scoring opportunity presented itself for the Mets on Tuesday. With two on and two out in the third inning, Wright skied a ball into center field. The hit didn't have home run distance, but it would have hit the wall for a pair of RBIs had Morgan not chased it down and made a leaping grab.
Aside from that situation, the Mets were unable to couple baserunners in an inning all night.
"We just got to get runs," Wright said. "It doesn't matter when they come. We need to do a better job of putting ourselves in more positions where we can drive runs in."
Mark Selig is an associate reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.