(Paul Sancya/AP)

The stunning decision comes one year after Lannan, twice the Nationals’ opening day starter, won 10 games with a 3.70 ERA. Lannan, making $5 million this season, is believed to be the highest-paid player in baseball history to be optioned to the minor leagues before the end of spring training.

Manager Davey Johnson had anointed Lannan the team’s fifth starter once Chien-Ming Wang suffered a hamstring injury midway through spring training, with Detwiler in the bullpen. It is not known for certain that Detwiler will join the Nationals’ rotation, but he is the only plausible candidate.

Detwiler, a former first round pick, has more raw stuff, including a fastball in the mid-90s, than Lannan. But Lannan, having thrown more than 180 innings three of the past four years, has more of a track record.

With Detwiler out of the bullpen, the Nationals will be able to give opening day spots to both Craig Stammen and Ryan Mattheus. Chad Durbin had been in the running, but the Braves announced this afternoon they have signed him to a major league deal, which means he opted out of his minor league contract with the Nationals.

General Manager Mike Rizzo did not immediately respond to a text message.

More to come when available.