Baltimore's loss to the Tennessee Titans Sunday left the Ravens defense frustrated and disappointed.

On a day where the offense struggled to muster much of anything, the defense had kept the Ravens within striking distance. The defense basically shut down the Titans in the second half, and forced three-straight three-and-outs and came up with a critical fourth-quarter interception to set up a touchdown.

The Ravens (4-5) suddenly trailed by only three points midway through the fourth quarter, but just when it seemed like they might mount a late-game comeback, the defense allowed the Titans to march down the field on a 75-yard touchdown drive.

"Our defense is not happy with [itself] about that one," Head Coach John Harbaugh said following the 23-20 defeat.

The 11-yard touchdown pass from quarterback Marcus Mariota to wide receiver Eric Decker put the Ravens in a 10-point hole they couldn't overcome, and the defense was left kicking itself on a day where it had otherwise played stout football.

"They made the right plays at the right time, and we messed up at the wrong time," inside linebacker C.J. Mosley said. "We played good defense, but if we would have gotten that stop, it would have been great defense. Sometimes that's the difference in games."

Mosley attributed the breakdowns on the last drive to "three mental errors." He pointed specifically to his missed tackle on running back Derrick Henry early in the drive that allowed the Titans to convert a third down.

"We want to be great all the time and we can't have those kinds of errors at points like that," Mosley said.

The late drive was particularly frustrating for the Ravens considering how well the defense had played the rest of the day. Tennessee's two previous touchdowns came on short fields after an interception by quarterback Joe Flacco and a shanked short punt by Sam Koch.

Outside of those drives, the defense had been strong.

"It was going pretty good most of the game, but we just have to finish out the game," Mosley said.

The Ravens allowed just 257 total yards, and only 71 yards came on the ground. Mariota finished the game 19-of-28 for 218 yards with two touchdowns and an interception.

The up-and-down nature of Sunday's game is indicative of how the entire season has gone for the Ravens defense. The group came into the season expecting to be one of the best units in the league, and they've shown that potential in shutout victories over the Cincinnati Bengals and the Miami Dolphins.

But they've also been gashed on the ground in losses to the Chicago Bears, Pittsburgh Steelers and Minnesota Vikings, and Sunday's loss was a disappointing development.

"You want to give your offense a chance to win the game or tie the game, and we did the one thing you can't do – give up points," outside linebacker Terrell Suggs said. "It's like we played pretty solid up until that drive. I don't know what happened, it's just very unfortunate."

The Ravens are built to rely on their defense, and they will need the unit to play stellar down the stretch if they are going to get back into the postseason. The group is filled with high draft picks and expensive free-agent acquisitions, and Suggs put it bluntly when discussing how the unit needs to improve.

"We expect to play lights out every week," Suggs said. "We got a bye week, then seven left. We better get the [stuff] fixed or we're going to be on the outside looking in again."