Redskins Coach Mike Shanahan conferred with his quarterbacks, John Beck and Rex Grossman, during Washington’s preseason game against Pittsburgh on Aug. 12. Nearly a month later, the starting job is Grossman’s. (John McDonnell/The Washington Post)

Now that Mike Shanahan is officially rolling with Rex in the season opener Sunday against the New York Giants, he needs to stick with him through the ups and downs of the NFL’s 16-game obstacle course. If the Redskins struggle, Shanahan should ignore the inevitable rumblings for a quarterback change. Barring injury or horrendous play, Grossman should be given a full season to direct the offense and grow with the new-look Redskins.

Shanahan owes it to Grossman to truly give him an opportunity to revive his career. Because of Washington’s instability at the game’s most important position last season, committing to Grossman for the long haul in 2011 is in the organization’s best interest.

Hey, my position was clear on Beck-Grossman. I advocated for Beck to start, in large part because of what Redskins’ people told me about how highly Shanahan and his son, Kyle, Washington’s offensive coordinator, have viewed Beck since he joined the organization. Also, after observing Beck in his first two preseason games, I thought his athleticism and potential were important.

Beck had to lose the job, some Redskins employees believed. His clunker in the preseason finale didn’t help. Obviously, no one could read Shanahan’s mind, and it was repeatedly stated Grossman could win the job. (I also know Mike really doesn’t appreciate my advice.)

Bottom line, Shanahan chose Grossman. The Redskins should rally around Rex, who’s getting a great second chance.

Although Grossman started 31 games for Chicago and helped it reach the Super Bowl after the 2006 season, something was missing from his six-year run there. Bears fans wanted more than Grossman seemed capable of providing. Even in the best of times, they dissected his every move. When the Bears won, the feeling was they did so in spite of their quarterback.

Being under the microscope like that isn’t easy. Such is life for quarterbacks, especially in big media markets, but Grossman faced an unusually high level of scrutiny and pressure. It’s the same old story with quarterbacks: They get too much of the credit for wins and too much of the blame for losses.

I’ve never left an interview with Grossman, however, believing he made excuses for his performance with the Bears. Straightforwardly, Grossman says the situation simply didn’t work as well as he hoped it would. He acknowledges he could have played better at times and was eager to see how things developed with the Redskins.

Despite what happened in Chicago, Grossman remains confident. When Shanahan announced Grossman would replace Donovan McNabb as the starter late last season, Grossman was certain he could thrive in the offense, he told me at the time, because it was well-suited for his skills.

He had no concerns, at least none he revealed publicly, about taking over for McNabb after playing in only six games, with one start, since the beginning of the 2008 season.

During the final three games in 2010, with Grossman as the starter, the Redskins went 1-2. Grossman wasn’t outstanding statistically. He did enough, though, to keep himself in the mix for the preseason battle with Beck.

His biggest contribution was validating the Shanahans’ belief that McNabb was the team’s main problem on offense. He showed that their scheme could still function just fine. Washington simply needed someone other than McNabb at the controls.

Grossman has pleased the Shanahans with his work ethic and willingness to accept their guidance. Beginning his ninth NFL season and third in Mike’s offense (Grossman was a backup in 2009 for Houston, which uses the same scheme), Grossman has much more game experience than Beck.

It’s understandable why all of that would be comforting to the Shanahans. Without a doubt, Grossman, regardless of being viewed as a failed starter by other teams, is a safer pick than Beck, especially after how Beck flopped against Tampa Bay.

The Redskins responded well on offense when Beck started for the first time against Indianapolis. He had some good moments against Baltimore. With a chance to grab what he wanted against the Buccaneers, Beck seemed to change. He became hesitant. He made poor throws. Beck had the look of what he is: Someone without much experience.

Beck needed to deliver a strong closing kick. Instead, he missed in the most important outing of his career.

Grossman could make it easy now on Shanahan by playing well and maintaining a grip on his job. That would be best for the Redskins, who seem to have made significant roster upgrades at many other positions.

Since Grossman has done everything the Shanahans have asked of him, they should give him every opportunity to work through rough stretches if they occur. They’re aware of Grossman’s limitations, and still picked him. So give him a chance to get it done.

The worst thing Mike could do now is go back and forth between Grossman and Beck. Doing so would stir more questions about his decision-making at a time the Redskins, for the most part, seem to be making more good ones than bad.

For Beck, it’s another disappointing development in a career still waiting to get started. Publicly and privately, Shanahan listed Beck among the reasons the Redskins did not draft a quarterback. He confounded some in praising Beck, who ultimately wasn’t good enough to beat out Grossman.

Daniel M. Snyder pays Shanahan a king’s ransom to make the right call on major decisions. Hopefully, for the Redskins and their fans, this one will turn out well.