NEW YORK — The Nationals have a grand slam with help from instant replay after a wild sequence against the New York Mets.

Josh Willingham's first-inning drive off the wall in left-center against Mets starter Johan Santana on Sunday was initially ruled a triple, with Willingham tagged out trying to score when the ball got away from catcher Rod Barajas.

After checking the replay, the umpires ruled it was a home run.

The top of the outfield wall at year-old Citi Field is about twice as high in left as in center. The orange line painted along the top is vertical where the sections meet, causing some confusion about whether the ball was in play.

Replays showed it hit just to the right of the vertical line and above the horizontal line, making it a home run.

Santana had loaded the bases with one out on a triple by Nyjer Morgan and walks to Willy Taveras and Adam Dunn, before Willingham drove a 2-1 pitch deep.

The ball caromed into center field and the relay throw eventually got to Barajas, who was plowed over by Dunn. The ball squirted free and Santana, backing up the play, threw it back just before Barajas got run over again — this time by Willingham. Barajas managed to tag him out.

The umpires then conferred for a moment before heading to the replay booth. Moments later, crew chief Derryl Cousins emerged to signal home run.