PITTSBURGH -- Once up 17 points early in the third quarter, the Pittsburgh Steelers' lead evaporated over the next quarter-and-a-half Sunday as the Philadelphia Eagles rattled off 15 unanswered points at Heinz Field.

Once responsible for carrying the team while the offense figured out its identity, the Steelers' defense nearly collapsed in the 38-29 win.

If the Eagles had completed the comeback, it would have been the biggest blown lead at home in Steelers history, according to ESPN Stats & Information.

The Steelers gave up 276 passing yards in the win -- in line with their weekly average -- but the bigger problem is that they gave up those yards to quarterback Carson Wentz and his cast of backup receivers.

Wide receiver Travis Fulgham, who entered the game with two catches for 57 yards, exploded for 152 yards and a touchdown on 10 receptions.

With the Cleveland Browns (4-1) and their receiving tandem of Odell Beckham Jr. and Jarvis Landry on the horizon, the Steelers have to figure out how to limit the big plays -- and fast.

And it's not just that the Steelers gave up the yards, it's when they gave them up.

The Eagles converted 10 of 14 third downs for a 71% efficiency -- including six of eight in the first half. That was the worst mark by the Steelers' defense all season. In the first three games, the Steelers (4-0) never allowed opponents to convert more than 53% of their third downs.

"Got to give Philadelphia a lot of credit, they tested us," coach Mike Tomlin said. "Their ability to convert third downs offensively, I thought, was a significant component of the game. Some of it was self-inflicted by us in penalties and missed tackles and so forth. You've got to give their guys credit. They had a good plan, good execution of the plan, and that allowed them to maintain possession of the ball and keep us at bay and stay in it."

The first significant third-down conversion was the Eagles' first. The Steelers held Wentz and Co. to consecutive three-and-out drives to open the game. On the Eagles' third possession, though, Pittsburgh native Miles Sanders took advantage of a blitz and broke through.

Nickelback Mike Hilton missed a tackle of Sanders on third down and the speedy back slipped through the hole and streaked down the field for a 74-yard touchdown.

"We just had an overload five-man blitz from the strong side," linebacker Vince Williams said of the play. "Teams are going to try to get us away from our blitz pressure because they understand that we are coming at quarterbacks on third down. That was a great game plan by them. We got to get them on the ground. Miles Sanders just did a great job."

After that score, the Eagles converted their final four third downs of the half, including one on a roughing the passer penalty called on Williams and a 20-yard completion to Fulgham on third-and-17.

The Steelers' knack of giving up big plays on third down continued into the second half.

Wentz found Fulgham again to convert a third-and-12 with a 31-yard completion to continue a drive that turned into a touchdown and a two-point conversion to bring the Eagles within nine.

On the next drive, Wentz went to Fulgham again on third and long, and this time the pair picked up 18 yards, continuing another eventual touchdown drive that whittled the Steelers' lead to two.

The Steelers allowed the Eagles to convert one more third down, a keeper by Wentz on third-and-2. But they came up with a big stop on third down later in the drive when Joe Haden broke up a pass from Wentz to Fulgham to force a failed field-goal attempt. On the Steelers' ensuing drive, quarterback Ben Roethlisberger found rookie receiver Chase Claypool for his fourth touchdown of the day, giving the defense a little room to breathe in something of a role reversal for the two sides.

Steelers defensive players couldn't diagnose the exact problem with the Eagles' third-down conversions, saying only that they would watch the tape later. Part of the problem could stem from the Steelers' penchant for blitzing more than any other NFL team, leaving receivers open downfield.

"I think it was a little bit of everything," linebacker T.J. Watt said. "I think we got to go back and look at the film and see where we can get better. I didn't get to see what happened at the back end or what happened at the front end. So, it's too early to say one specific thing."