More important to the Redskins this season, Shanahan appears to have been telling the truth when he said last season that Grossman, who had played in just 38 NFL games in nearly eight seasons before replacing McNabb at the end of last year, was a better fit for the offense that his son, Kyle, the offensive coordinator, wanted to run.
McNabb's passing for just 39 yards in his debut with the Minnesota Vikings probably supports that, too, but that's another story.
Against the Giants, Grossman completed 21 of 34 passes for 305 yards and two touchdowns.
"It feels good," Grossman said. "We scored 21 points on offense and that's pretty good. It's not exactly where we want to be, but it's pretty good."
For most of his career, Grossman was best known for being a running joke as a failed first-round pick of the Chicago Bears - even though he did lead them to the Super Bowl in the 2006 season.
Even coming into this season, Grossman, who had started only four games since 2007, hadn't really inspired overwhelming confidence.
Redskins fans were 50-50 on whether they wanted Grossman or fellow journeyman John Beck as their quarterback. "Neither of the above" was not an option.
"I thought [Grossman] played an excellent game," Shanahan said. "There was a lot of pressure up front from that defensive line, and it was hard to make big pass plays against that defense."
Given his mostly failed history, nobody is going argue that Grossman, 31, has proved he is a competent NFL quarterback after one good game of a long season.
Still, in his five appearances as a Redskin, Grossman has now completed 95 of 167 passes (.569) for 1,189 yards and nine touchdowns.
"Things don't always work out the way you think they will to start a game," said Grossman, who missed his first four passes, "but you stick with it and you will get into a rhythm."
In the bigger picture of what this game means to the NFC East, the Redskins look like they might be better than many people think while the Giants might be a bit more vulnerable.
Grossman and the Redskins looked like they were playing against a team that was missing four projected starters on defense, which they were.
The Redskins outscored the Giants by 14-0 in the second half.
"I wouldn't say that something is off," Giants safety Antrel Rolle said of the final 30 minutes. "There were times we shut them down and there were times when they made good plays. They get paid just like we do.
"At the end of the day, we tried to be effective with what we do as a unit. I think it is more about us and not so much about them."
It was definitely a lot about Giants quarterback Eli Manning, who started the 2011 season at the same place he was in 2010.
After being plagued by 25 interceptions last season, Manning made the decisive blunder to start this year.
With the score 14-14 in the third quarter, Manning tried to throw a pass to Hakeem Nicks, but Redskins rookie defensive end Ryan Kerrigan tipped the pass, then intercepted it and finally ran 9 yards for what would ultimately be the game-winning touchdown.
"Up until halftime, it was a very, very good and competitive football game," Giants coach Tom Coughlin said. "To start the second half off with an interception for a touchdown . . . that's a tough way to start the second half.
"I did not like the end of our game offensively at all. Offensively, we didn't do a thing. We didn't score a point. That was very disappointing. It's our first game. I liked the effort. I had no problem with that at all, but the execution, particularly the offensive execution and the inability to defend the pass of play action, was disappointing."
The Redskins have been here before. Last year, they beat Dallas in the first game of the Shanahan era, only to finish 6-10.
Washington has only two playoff appearances and two winning seasons in the past dozen seasons. The Redskins haven't won a division title since 1999.
"As I told our team, I've got a lot of confidence in them," Shanahan said. "But you have to take it one game at a time. There is a lot of football left to play.
"Talk is cheap. You have to go out there and prove yourself."
Grossman did - for at least 1 week.
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