President Barack Obama was high and wide. Roy Halladay was right on target -- as always.

The Phillies backed their new ace with plenty of power, too.

Placido Polanco hit a grand slam, Ryan Howard also homered, and Halladay struck out nine over seven innings in his National League debut as the Phillies opened the season Monday afternoon with an 11-1 rout of the Washington Nationals.

The centerpiece of the Phillies' drive for a third straight World Series appearance, Halladay (1-0) allowed one run and six hits and settled down to dominate after the Nationals scored in the first. Ivan Rodriguez doubled to lead off the second, but Halladay then faced the minimum number of batters -- with help from a pair of double plays -- until the seventh, when he worked out of a two-on, one-out jam.

Making his eighth consecutive Opening Day start, Halladay even helped himself at the plate with his second career RBI, albeit on a dribbler that traveled all of about 30 feet in Philadelphia's five-run fourth inning. He had plenty of support from a sellout crowd that was as much pro-Phillies as pro-Nationals.

The crowd more united in its support for Obama, with only some scattered boos among the thunderous cheers as he took the mound to mark the 100th anniversary of presidential first pitches. Not a natural baseball player by his own admission, the left-hander -- wearing a Nationals jacket but a Chicago White Sox cap in a nod to his favorite team -- double-clutched before uncorking a wayward delivery that had third baseman Ryan Zimmerman standing and stretching his arm just to make the catch.

"It was high and outside. I was intentionally walking the guy," Obama quipped during an appearance in the booth during the Nationals' TV broadcast. "Fortunately, Zimmerman has a tall reach."

On April 14, 1910, when William Howard Taft became the first president to take part in a first-pitch ceremony, The Associated Press story opened with the following sentence: "President Taft today enjoyed the novel experience of seeing the Washington American League team win a ball game."

Obama had no such luck. The 1910 Washington team wasn't very good, and the 2010 National League version started off looking like the same old crew that lost 100-plus games in 2008 and 2009.

John Lannan (0-1), the Nationals' opening day starter for the second year in a row, lasted only 3 2-3 innings, allowing five runs and seven hits with three walks and no strikeouts. He was done in by a morale-sapping fourth inning, when eight of the 10 battered he faced reached base. By then, Obama had left the ballpark.

The big hit was Howard's homer, which reached the first row of the middle deck and was followed by singles from Jason Werth, Raul Ibanez and Shane Victorino. After a flyout, Halladay come through with the dribbler that Lannan scooped and unsuccessfully shoveled toward the plate in an attempt to keep Ibanez from scoring.

Polanco's second career slam came in the seventh off Jason Bergmann. Polanco went 3 for 5 and had a career-high six RBIs.

Notes: The Phillies broke a streak of four consecutive opening day losses. ... When the Nationals scored in the first, it broke Halladay's 24-inning scoreless streak over his last three starts with the Toronto Blue Jays. ... The loss ended the Nationals' majors-best seven-game winning streak from the end of last season. ... Zimmerman, Adam Dunn and Lannan were the only three Nationals starters from their opening day lineup a year ago. ... Rodriguez made his 19th consecutive opening day start, the longest streak in the majors. He had three hits, including a pair of doubles. ... Ian Desmond, Washington's new starting shortstop, made an error on the first ball hit to him. Only an alert play by first baseman Dunn kept a run from scoring as the Nationals went the 6-3-2 route to record the final out of the first inning. ... The Phillies were without first base coach Davey Lopes, whose brother died in a house fire in Rhode Island on Friday. Manager Charlie Manuel said he expects Lopes to be back after the current six-game road trip. ... Zimmerman was awarded his Gold Glove and Silver Slugger awards before the game. He and OF Matt Kemp of the Los Angeles Dodgers were the only National Leaguers to win both last year. ... Commissioner Bud Selig tried to put a positive spin on the disproportionate number of Phillies fans in the ballpark. ``I think it's great for the sport, I really do,'' he said. "There's enormous interest, obviously, in Philadelphia and the fact that people travel as much as they do now. ... It's only a testament to this game's popularity.'"