Harper will try to help the Nationals beat the New York Mets for the eighth time in nine games Wednesday night in the nation's capital.Harper is one of the best young players in baseball at 19, hitting .288 with five homers, 14 RBIs and a .528 slugging percentage since being recalled from Triple-A Syracuse in late April. He's done much of that damage over the last 13 games, batting .373 with three homers, three triples and a .458 on-base percentage.He collected two more hits Tuesday, driving in Jesus Flores in the 12th inning to give Washington (31-22) a 7-6 win over New York to open this three-game set."He's a man-child," Michael Morse said of Harper. "This guy's unbelievable. He's really learning this game. Every day, I think he's taking something in. When he plays like he plays, it's fun to watch and it's good to have him on our side."Edwin Jackson (1-3, 3.17 ERA) could use some help from the rookie if he's going to get his first victory since beating Cincinnati on April 14.The right-hander is 0-3 with a 3.33 ERA in eight starts since. He's received two total runs of support while going 0-2 with a 2.08 ERA in his past three outings.Jackson yielded two runs -- one earned -- and five hits in 6 2/3 innings May 29 at Miami. However, he allowed the go-ahead run in the seventh after a wild pickoff throw to first allowed Chris Coghlan to advance to third before scoring on a sacrifice fly.The Mets (31-25) are trying to avoid a third consecutive loss, and they can start by putting Tuesday's three errors and two wild pitches behind them. Three of those miscues came in the 10th when they squandered a 5-4 lead."The toughest part is the way we fought back," manager Terry Collins said. "You're down three. We fight back. We get the lead. We lose the lead, get the lead, lose the lead, we get the lead and then we lose the game. That's very tough."Collins is scheduled to turn to Jeremy Hefner (1-2, 5.60) in place of Johan Santana, who has been pushed back to Friday's Subway Series opener with the New York Yankees after throwing a career-high 134 pitches in the Mets' first no-hitter last week.Hefner made history of his own in his last trip to the mound May 29, getting his first career victory in a 6-3 win over Philadelphia. The right-hander yielded three runs in six innings while helping himself with a solo homer for his first career hit.He's the first Mets pitcher to homer in his first victory, and the first major leaguer to accomplish that unusual feat since Dennis Tankersley with San Diego in 2002."Obviously I want to be here," Hefner told the team's official website. "If I'm better suited in Triple-A, I understand that. But if I'm here, I'm going to give it my all, and I'm going to do everything I can to win ballgames."The Mets may have Jason Bay back from a broken rib that's kept him out since April 23.