Jose Guillen was plunked twice by Pedro Martinez, and the second time he slowly approached the mound, waving his bat, but was restrained. The tensions escalated after Guillen said things could get ugly if Martinez hit him again.
The warning gives the umpiring crew the discretion to eject a pitcher without warning if he feels a pitch was thrown with intent at a batter.
"They've always had that (authority)," Mets manager Willie Randolph said. "Your hands are tied. There's nothing you can do. You have no control over it."
REPLAY: Pedro Martinez is always the focal point in every game he pitches. It was that way in Wednesday night's 3-1 victory over the Nationals, a team he faced last week at Shea Stadium and hit three batters, including Jose Guillen twice.
Guillen threatened mayhem if he were hit again, and he had a chance to extract his revenge when he came up with the bases loaded and one out in the sixth.
Martinez fell behind 2-and-1 before getting Guillen to ground into an inning-ending double play.
The Mets ace got the win, allowing three hits and one run in seven innings.
A strained right quad muscle in May and facial fractures sustained in an August collision with Mike Cameron contributed to Beltran's season in which he hit a very pedestrian .266 with 16 homers and 78 RBIs.
Beltran was booed Opening Day and for much of the first homestand when he was held hitless in his first nine at-bats.
His reception figures to be much better when the Mets return for their second homestand this weekend against the Brewers.
Beltran said he's more relaxed at the plate, as evidenced by a five-game stretch last week in which he hit two homers and drove in eight runs.
"I've been swinging the bat better," Beltran said. "I'm seeing the ball and getting a good swing on it."