The Washington Redskins kicked off Year 2 of the Mike Shanahan Era in victorious fashion Sunday, thumping their NFC East rival, the New York Giants, 28-14, in a rather un-Redskins-like performance that featured fireworks on offense, heroic defense and clutch special teams contributions.

Looking drastically different from the team that staggered through the 2010 season plagued by an ineffective attack, a leaky defense and poor field position, the Redskins orchestrated scoring drives on critical possessions and held the visiting Giants in check when it mattered most. Then they slammed the door with a 70-yard, fourth-quarter scoring drive.

“It felt great to finish,” said wide receiver Anthony Armstrong, who caught one of two Rex Grossman touchdown passes on the day. “Last year, I don’t know that we would’ve scored on those plays. . . . It’s different this year: attitude and something that’s going on in this locker room that I can’t explain.”

Grossman — the ninth-year veteran, who started the final three games of the 2010 season after the failed Donovan McNabb experiment, then beat out John Beck for this year’s first-string duties — led the offense. He completed 21 of 34 passes for 305 yards, two touchdowns and no interceptions as he spread the ball around to six different targets.

On defense, the Redskins flustered Eli Manning and the Giants, holding them scoreless in the second half and forcing Manning to to throw an interception as he completed just 18 of 32 passes for 268 yards.

Even the two-touchdown margin of victory before an announced crowd of 80,121 was a rarity for Washington, which in the previous 48 games had won by more than seven points only once.

In the offseason, Washington sought personnel who better fit in Shanahan’s offense and defensive coordinator Jim Haslett’s defense. The moves purged Washington’s roster of big names and familiar faces, such as McNabb, Clinton Portis, Albert Haynesworth and Carlos Rogers, leaving Washington with a younger, more willing and able roster.

But the offense went three-and-out on its first two possessions of the game, and Grossman was 0-for-4 passing on those two offensive outings.

Manning also missed his first four pass attempts, but struck on a 68-yard pass to Hakeem Nicks to set up his team’s first score. On third and 10 from the New York 30-yard line, Washington’s defense lined up in a two-deep zone coverage, and cornerback DeAngelo Hall released Nicks to strong safety Reed Doughty. But Doughty appeared to slip initially and couldn’t catch up to Nicks, who made the catch and fell out of bounds at the Washington 2-yard line. On the next play, Manning rolled out to his right and tip-toed into the end zone to cap a four-play, 70-yard scoring drive.

Grossman and the Redskins found a rhythm on their third possession, marching 62 yards to the New York 16-yard line in nine plays, including three completions by Grossman. But Grossman was sacked for a five-yard loss, and then led Armstrong out of bounds for his first incompletion of the drive.

Washington had to settle for a 39-yard field goal attempt, but Graham Gano — who was perfect in the preseason — missed wide right.

The Giants didn’t capitalize on Washington’s error, however, and punted five plays later.

The Redskins came back for their first scoring drive of the season. Paced by four Grossman passes, Washington marched downfield. Armstrong made a diving 18-yard catch at the 1-yard line and Tim Hightower scored on a sweep to the left to cap the 11-play drive, tying the score with nearly a quarter left in the first half.

“Things don’t always work out the way you think they will to start the game, but you always have confidence that you can get into a rhythm,” said Grossman, who previously had thrown for more than 300 yards in a game only three times (twice for Washington last season). “Nothing changed. The game just went along and eventually things got going.”

Grossman was better still with time running out in the second quarter. With 2 minutes 48 seconds to work with and the ball at his 20, Grossman led the Redskins on an 80-yard drive while completing all five of his pass attempts. Grossman’s longest completion was an under-thrown pass to Jabar Gaffney, who was wide open and streaking up the left sideline. Gaffney had to come back for the throw and was tackled for a 39-yard gain.

Two plays later, Grossman connected with Armstrong from six yards out with 43 seconds left on the clock for his first touchdown pass of the season. Gano’s point-after attempt tied the game at 14 heading into the half.

Purdue’s Ryan Kerrigan, selected in the first round in the belief that he could convert from defensive end to outside linebacker and complement Brian Orakpo, made a memorable NFL debut. With the Giants facing third and 10 from their 18-yard line, Kerrigan blitzed and batted a Manning pass into the air. The 6-foot-4, 263-pound rookie caught it at the 9 and rumbled into the end zone for his first interception and touchdown in the NFL.

Another rookie, seventh-round draft pick Chris Neild, recorded two third-quarter sacks while giving starter Barry Cofield a breather at nose tackle on two different series.

Later in the quarter, Washington’s defense delivered again. With the Giants facing fourth and one from the Washington 31, Ahmad Bradshaw ran into a wall of Redskins for a loss on downs.

The defense bailed out the sputtering offense yet again in the second half. Grossman — a play after nearly throwing an interception — fumbled the ball as he was sacked by New York defensive end Jason Pierre-Paul, and linebacker Michael Boley recovered it at the Washington 27.

The defense forced another three-and-out, bringing on the Giants’ field goal unit. But Orakpo blocked Lawrence Tynes’s attempt, and London Fletcher recovered it at the 30-yard line.

Sparked by the defensive stand, Washington’s offense marched 70 yards in 10 plays and found the end zone on a four-yard pass from Grossman to Gaffney, his former college teammate, for a touchdown that clinched the 28-14 victory.