Dolphins coach Joe Philbin wouldn’t commit to quarterback Ryan Tannehill moving up to No. 2 on the depth chart following a 20-7 preseason loss to Tampa Bay on Friday. But he did acknowledge the gap between the rookie and incumbent Matt Moore is closing.

“I don’t think it’s huge,” the first-year Miami coach said. “I think it’s relatively close.”

Moore, who led the team to a 6-3 record down the stretch last season as he threw for 2,497 yards with 16 touchdowns against nine interceptions, started in place of veteran Pro Bowler David Garrard. The 34-year-old sat atop the team’s depth chart after two weeks but announced just before kickoff he would be undergoing knee surgery that could sideline him for up to four weeks.

Moore, however, couldn’t take advantage of the start. The six-year veteran completed 7 of 12 passes for 79 yards with an interception. Meantime, Tannehill, who played mostly with second- and third-teamers, completed 14 of 21 passes for 167 yards and a touchdown. 

“It’s small steps, just going out and trying to be the best QB that I can be,” the eighth-overall pick in April’s draft said. “At the end of the camp, then it’s up to the coaches.”

Johnson debut: Chad Johnson was hoping his first catch in a Dolphins uniform would come before his first drop.

But the former Pro Bowler couldn’t hang onto what appeared to be an easy catch early in the first quarter that would have moved the chains on third down. Instead, kicker Dan Carpenter shanked the first of two field goals. Not the debut either veteran was looking for on Friday night against Tampa Bay.

“We have a long way to go and have a lot of room for improvement,” Johnson said. “It’s really hard to assess most of the game looking at it from the naked eye on the sideline, but it looked good and I am sure that there will be a lot of corrections.”

Offensive defense: Philbin has a simple message for his defense: tackle.

The unit routinely missed open-field tackles in the loss to Tampa Bay as they allowed 269 yards and didn’t record a sack. Philbin said the coaching staff had emphasized the importance of wrapping up and he was disappointed in a defense he claimed to not recognize after two weeks of strong practice.

“We think we spent a lot of time on tackling, we spent a lot of time on pursuit and angles and those types of things,” Philbin said. “It wasn’t up to our standards.”

One of the biggest culprits was cornerback Sean Smith, who missed a pair of stops in addition to getting beat early on a deep ball that led to a Buccaneers’ touchdown. The poor tackling also enabled Tampa Bay to convert 8 of 15 third-downs and maintain a 33:29 to 26:21 edge in time of possession.

“Just the simple, basic football,” defensive end Cameron Wake said. “I think that’ll be something we’ll work on this week coming up.”

For more up-to-the-minute news and analysis on the Miami Dolphins from blogger Dave Carey, follow @CBSSportsNFLMIA.