NEW YORK -- After almost 4 hours of baseball filled with twists and turns, Matt Williams has his first win as a major league manager.
Anthony Rendon hit a three-run homer in the 10th inning and had a career-best four RBIs, twice rallying the Washington Nationals against the New York Mets' suspect bullpen for a 9-7 victory in their season opener Monday.
''I have a stomach ache right now,'' Williams said. ''There was lots of stuff today. I feel right in the thick of it.''
Denard Span hit a tying double with two outs in the ninth off closer Bobby Parnell, and Ian Desmond put the Nationals in front for the first time with a sacrifice fly in the 10th. Rendon connected two batters later against former Washington pitcher John Lannan, securing a win for Williams in his managerial debut.
''I'll probably sleep good tonight,'' Williams said. ''That's what we want to have as our DNA -- never give up, never give in.''
Stephen Strasburg struck out 10 over six innings in his third straight opening-day start. But he fell behind early and was outpitched most of the day by Dillon Gee, given the starting assignment because of injuries to Matt Harvey and Jonathon Niese.
Nationals star Bryce Harper was shaken up in the second inning when he got kicked in the forehead by second baseman Eric Young Jr. while breaking up a double play. Harper stayed down for a minute or two and rubbed his head after Williams and a trainer rushed out to check on him. The young slugger stayed in the game, though, and later began Washington's comeback.
''I'm OK, but I've got a pretty bad headache right now. I was seeing stars there, but I've seen stars before,'' said Harper, who passed concussion tests during and after the game.
Aaron Barrett (1-0) struck out two in a perfect inning to win his major league debut, with family in the stands.
''It was such an amazing team win,'' he said. ''It was awesome to be a part of it.''
Lagares put New York ahead 5-4 with a leadoff homer in the eighth against Tyler Clippard, but the Mets couldn't hold it. Parnell failed in his first save opportunity since neck surgery for an injury that sidelined him for the final two months last season.
The Mets lost for only the third time in their last 23 season openers at home. They still own the best mark in the majors on opening day at 34-19.
The temperature at first pitch was 44 degrees, with wind gusting to 25 mph, but it warmed up as the sun came out. Gee pitched in short sleeves and retired 15 in a row after Adam LaRoche's long two-run homer in the second. Harper snapped the streak with a hard-hit infield single in the seventh.
''We got a great performance today by Dillon. Unfortunately, we couldn't get him a win,'' Wright said. ''There's some things that we need to work on moving forward and that was pretty glaring in game one.''
Rendon, the new starter at second base, chased Gee with a two-out RBI double. Washington tied it 4-all when relievers Carlos Torres and Scott Rice issued consecutive four-pitch walks, forcing in a run.
''That situation, I can't let that happen,'' Rice said.
Brown, a surprise starter in left field because newcomer Chris Young sat out with a mild right quadriceps strain, hit a three-run shot to left-center on a 94 mph fastball from Strasburg in the first inning.
''They came out swinging, and I missed with some stuff that was off the plate,'' Strasburg said.
Chris Young's injury also opened a spot for Lagares, who started in center. Eric Young, normally the left fielder, shifted to second base to fill in for Daniel Murphy, who was in Florida with his pregnant wife awaiting the birth of their first child.
Eric Young had a sacrifice fly in the second.
Nationals C Wilson Ramos left in the seventh after being hit on the hand by foul ball. X-rays were negative and he will see a hand specialist Tuesday. Ramos was replaced by Jose Lobaton, who singled during the decisive rally. ... After an off day Tuesday, Chris Young and Murphy are both expected back in the lineup Wednesday night, when RHP Bartolo Colon makes his Mets debut against LHP Gio Gonzalez. ... Williams challenged a fairly close play at first base that ended the top of the 10th. Umpires confirmed Clint Fagan's call with instant replay.