(AP) -- Anthony Rendon hit a three-run homer in the 10th inning and drove in a career-high four runs, twice rallying the Washington Nationals against the New York Mets' suspect bullpen for a 9-7 opening-day victory Monday.

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 Matt Williams in his first game as a major league manager.

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 starter Dillon Gee, given the assignment because of injuries to Matt Harvey and Jonathon Niese.

Several fill-ins came through for New York, in fact. Juan Lagares and Andrew Brown both homered after they were surprise additions to the lineup.

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. But the young slugger stayed in the game and later helped Washington begin its comeback.

Aaron Barrett (1-0) struck out two in a perfect inning to win his major league debut.

Jeurys Familia (0-1) took the loss, hurt by catcher Travis d'Arnaud's passed ball. David Wright hit a two-run homer in the 10th.

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.

After playing 20 extra-inning games last season, including a 20-inning loss to Miami, the Mets were right back at it. They entered with the best mark in the majors in season openers (34-18), but lost for only the third time in their last 23 season openers at home.

Umpires used instant replay to review a fairly close play at first base that ended the top of the 10th. The call was confirmed.

New Yorkers woke up to an icy mix of sleet and snow flurries -- only fitting on opening day after the frigid winter much of the country endured. The temperature at first pitch was 44 degrees, with wind gusting to 25 mph, but it warmed up as the sun came out in the afternoon.

Both teams took batting practice indoors but the tarp was removed in plenty of time to start right on schedule. 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. Rendon, the new starter at second base this season, chased Gee with an RBI double and the Nationals tied it 4-all when relievers Carlos Torres and Scott Rice issued consecutive four-pitch walks, forcing in a run.

Brown, a surprise starter in left field because newcomer Chris Young sat out with a mild right quadriceps strain, clubbed a three-run shot to left-center on a 94 mph fastball from Strasburg in the first inning.

Chris Young's injury also opened a spot for Lagares, who started in center. Eric Young, normally a 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.

NOTES: It was LaRoche's 11th homer at Citi Field, tied with Atlanta 2B Dan Uggla for the most by an opposing player, according to STATS. ... Mets RHP Jenrry Mejia (bruised forearm) is on track to make his scheduled start Friday night against Cincinnati, manager Terry Collins said. ... 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. ... Late slugger Ralph Kiner, a Hall of Famer and Mets broadcaster since the team's inception in 1962, was honored before the game. The team unveiled a logo behind the left field fence that depicts Kiner's name, an old-fashioned microphone and the years 1922-2014. The same logo, also painted on the grass behind home plate, appears on the sleeves of Mets uniforms this season. Kiner died in February. ... New York City Mayor Bill de Blasio threw out the ceremonial first pitch.