Much has been made this season, and deservedly so, of the improvement by the Eagles' offense on third down.

But their defense also has been doing an impressive job of getting off the field on third down during the team's 7-1 start.

Jim Schwartz's unit went into Sunday's game against the winless 49ers ranked third in the league in third-down defense, behind only Denver and Minnesota.

It turned in another impressive third-down performance in the Birds' water-logged 33-10 win at the Linc, allowing the Niners and their rookie quarterback, C.J. Beathard, to convert just three of 15 third-down opportunities.

Beathard completed just five of 12 third-down passes for 34 yards. Cornerback Jalen Mills intercepted Beathard on a third-and-7 play late in the first half and returned it 37 yards for a touchdown that gave the Eagles a 17-0 lead.

It was the Eagles' eighth interception of the season, six of which have come on third down. That's the most third-down interceptions in the league.

"If you want to be a good team, you have to stay on the field on third down [on offense] and get off the field on third down [on defense],'' safety Rodney McLeod said.

Last year, the Eagles finished tied for 19th in third-down defense, allowing opponents to convert 40 percent of their third-down opportunities. With Sunday's impressive 3-for-15 performance, they have held teams to a 31.0 success rate in the first eight games.

Opponents have a 47.1 passer rating on third down against the Eagles. They've completed just 54.2 percent of their third-down attempts and have converted just 23 of 45 third-down completions (51.1 percent) into first downs.

And then there are those six third-down interceptions, three of which have been by Mills.

On Sunday, the hours of film work the cornerback spent during the short week (they played on Monday night) helped him read the out route that wide receiver Pierre Garcon ran and anticipate the throw from Beathard. Mills alertly jumped the route and picked off the pass.

"I've been watching film hard all week,'' Mills said. "Been kind of studying that route, too. Knowing Pierre Garcon, he's their possession receiver and also their best route runner.

"Seeing the motion go over to the single-receiver side, knowing the rookie quarterback was going to try to work him, as soon as I got the [route] stem that I've been seeing all week on film, I kind trusted my technique, trusted my feet and my safety over the top and jumped the route and picked the ball off.''

The Eagles' overall pass-defense numbers this season aren't great. They went into Sunday's game ranked 30th in passing yards allowed (272.9), 24th in touchdown passes allowed (12), 18th in opponent passer rating (89.1) and 17th in yards allowed per attempt (7.0).

But on third down, when they've needed a stop, they've been gold. Just two of their first eight opponents have managed to convert more than 40 percent of their third-down tries against them  —  Kansas City (41.7) and the LA Chargers (50.0).

In their last four games, including Sunday, opponents are a collective 15-for-57 (26.3%) against the Eagles on third down.

"We have a lot of guys who can rush [the passer],'' defensive end Chris Long said. "[There's been] good play-calling from Jim, and the cover guys are playing well.

"The under guys are tackling and knocking things down when people throw short and quick because they're afraid of the rush. So we've done a good job in a lot of areas.''

The Eagles' ability to stop the run also has helped. Even on third-and-short, opponents are throwing the ball. In their win over the Redskins last week, Jay Gruden called passes on a pair of third-and-1s and a third-and-2. They failed to convert all three tries.

On Sunday, just four of the Niners' 15 third-down situations were 3 yards or less. They threw on three of them and converted just one.

Two times, the Eagles' forced incompletions. On a third-and-one, Beathard tried to pick up the first down on a quarterback sneak. But defensive tackle Beau Allen got penetration and blew up the play.

"We put a lot of emphasis, spend a lot of time on preparation, for third down during the week,'' safety Malcolm Jenkins said. "Our game plan, our execution, and then once we get to the game, our ability to win one-on-one matchups [have been the difference].

"The ability to play the situation, whether it's third-and-short or third-and-long. Our defensive front has a lot to do with that. And the guys on the back end making plays. It's been the calling card of this defense this year. Getting off the field, getting drives stopped.

"Today, it was really important. Close game [for a while]. Weather was bad. We thought we could win on third down, especially if we could get them to third-and-three or more. Obviously, we were able to do that.''

Schwartz blitzed Beathard a few times on third down, but mostly relied on his front four to get pressure on the rookie.

Fletcher Cox sacked Beathard on a third-and-6 on the possession before Mills' interception. Long had a third-and-5 sack negated by a Niners timeout call.

"Quarterbacks, their clock is speeding up because they know we can rush,'' Long said. "They're getting that ball out quicker than they want to. And that's helping our cover guys make plays.''