It's been a long time since there was any doubt over the San Francisco 49ers' starting quarterback.

The picture behind Brock Purdy on the quarterback depth chart was less clear going into training camp and preseason.

San Francisco re-signed Brandon Allen and brought in Joshua Dobbs this offseason after Sam Darnold left to sign with the Minnesota Vikings.

Given how Dobbs played on short notice for the Vikings last year and, prior to that, how he performed for a surprisingly feisty Arizona Cardinals team, he might have been expected to win the QB2 job.

But Allen, with a year of experience in Shanahan's system, was the more consistent quarterback in training camp. 

Dobbs had the highlight reel plays in the preseason, but Shanahan confirmed on Thursday that Allen would be the second-string quarterback for the 49ers' season opener against the New York Jets on Monday.

Shanahan did not explain his reasoning for that decision, but he is on the record as valuing training camp practices above preseason games.

As such, Allen's early superior impression in camp looks to have given him a decided edge.

It would be interesting to see whether Shanahan would stick with Allen were Purdy to go down with an injury given the upside Dobbs offers as a playmaker. The 49ers, though, will have no desire for the team and their head coach to be put in that position in another 'Super Bowl or bust' season.

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It has only strengthened their evaluation of him.