The Dolphins’ three-way quarterback derby is apparently now a two-man race.

That’s because David Garrard, the anointed front-runner expected to start the Dolphins’ 20-7 exhibition loss to the Tampa Buccaneers, is out of the running for the foreseeable future.

Garrard missed Friday night’s exhibition opener with a surprise knee injury and needs arthroscopic surgery, his agent confirmed Friday evening. Garrard is expected to go under the knife Saturday morning and will miss between two and four weeks. Miami opens the regular season Sept. 9 at Houston.

“The timing stinks,” said Garrard’s agent, Al Irby.

Certainly for him. Unless Garrard makes a speedier-than-expected recovery, the Dolphins’ quarterback options are down to this: Either go with their hit-or-miss incumbent — Matt Moore — or hand the reins to the promising rookie.

Should Ryan Tannehill keep playing like he did Friday, he might make the decision easy for coach Joe Philbin. Tannehill, the first-round pick and heir apparent, simply moved the offense best, completing 14 of 21 passes for 167 yards in less than two quarters of action.

“I just went out there and played my best,” Tannehill said afterward. He didn’t take the bait when asked if he showed enough to be the starter going forward.

Quipped Moore: “I think it’s clear that he can play.”

Obligatory disclaimer: Tannehill — clearly the fan favorite, if crowd reaction is any gauge — played exclusively against Buccaneer backups.

But impressive throws are impressive throws, and none was prettier than his 19-yard completion to Roberto Wallace midway through the third quarter. Tannehill, showing command of the Dolphins’ hurry-up offensive, took a step to the right, then dropped a bullet over the defense and into Wallace’s breadbasket.

He later capped the nine-play, 70-yard drive with an 11-yard scoring pass to Charles Clay, the first touchdown (albeit in the preseason) of Tannehill’s pro career. For about five minutes, Tannehill looked to have an earlier one. Late in the first half, he hooked up with Wallace for what was initially called a 7-yard touchdown, but later overturned.

Meanwhile, Moore — playing against Tampa Bay’s starting defense — had an up-and-down night, a microcosm of his effectiveness since the start of training camp.

Moore, who led the Dolphins to wins in six of their final nine games last year, was 7 of 12 for 79 yards, with a hard-luck interception.

After directing the Dolphins to the Tampa Bay 21, Moore had an pass deflected by Frank Okam and intercepted by Lavonte David. It was the last pass he threw.

“I don’t think it’s huge,” Philbin said, when asked about the gap between his two healthy options. “It’s relatively close, probably.”

If Moore wins the starting job, it’s seemingly good news for Anthony Fasano, who on this night was Moore’s preferred target. Fasano caught three passes for 29 yards in limited action.

Meanwhile, Chad Johnson was noticeably quiet in his Dolphins debut. Johnson, looking to rehabilitate his career in Miami, was targeted just once — dropping an on-target pass that would have moved the chains.

Julius Pruitt led all Dolphins receivers with six catches for 52 yards, and Wallace added four for 71. Meanwhile, the Dolphins struggled on the ground, gaining just 43 rushing yards and averaging a paltry 2.9 per carry.

As for Garrard, the injury is particularly puzzling, considering he participated fully in practice through at least Wednesday, the last session open to the public.

Reached by phone just before Friday’s loss, Garrard told The Miami Herald he planned to take a “wait-and-see position.”

“I’ll be all right, though,” he added.

Garrard would not disclose to The Herald how or when the injury occurred, but told Fox Sports’ Jay Glazer that he had “loose things floating around” his knee that needed to be removed. Garrard hasn’t played a regular-season game since late in the 2010 season, missing all of last year with a significant back injury.

When asked about Garrard’s injury Friday, Philbin declined comment.

Miami Herald sportswriter Armando Salguero contributed to this report.