Doug Pederson needed to keep his offense on the field longer than he  planned just to see it register a first down in a 20-16 win over the Buffalo Bills on Thursday night, a bad sign for a unit that played without Pro Bowl left tackle Jason Peters and introduced top wide receiver Alshon Jeffery.

As fruitless as Carson Wentz and the starting offense appeared in the second preseason game of the  summer, the defense continued to excel. The starters forced turnovers on two of their first four drives, including an interception by new cornerback Ronald Darby against his former team.

Preseason football offers observations about players all the way down the depth chart, but the most significant ones happen in the first quarter. That's when the starters play, and it's those players who will determine what kind of autumn it will be in Philadelphia.

"Was the performance great? By no means, it was definitely not where we want to be," Wentz said, "But I definitely don't have doubts. I know we have the right guys. We have the right scheme. We've just got to put it together."

Pederson said  Tuesday that his offense would likely play a series or two, although it always depends on game situations. A 90-yard drive can offer a coach enough for an evaluation. A three-and-out begs for more action. The offense begged again and again and again.

"We don't game-plan these games," Pederson said. "We just rep our training camp plays. We're trying to see and evaluate our players still. …Sometimes, too, guys know there's a limited number of reps, so they expect maybe a certain style, and if it's not there, it's hard to get into the flow of the game."

There was excitement at Lincoln Financial Field when the offense took the field because it was Jeffery's first game action with the Eagles. He missed last week's outing while Pederson exercised caution during Jeffery's recovery from a shoulder injury, and Wentz was eager to play with his new top receiver Thursday. Jeffery was the target on the second pass of the game, but it sailed over his head. The same happened on the next drive, when Wentz tried to find Jeffery in the end zone, although the receiver  was well-covered.

On the offense's fourth drive, Wentz and Jeffery finally connected. A quick throw to Jeffery netted 9 yards, and then Wentz found Jeffery on the run two plays later for 14 yards. Jeffery, wearing white  cleats, showed the promise that made him the Eagles' top free-agent target at the position. They  hope to see that connection about 80 times this season.

The other high-profile, skill-position player the Eagles added on offense was LeGarrette Blount, and it was not the best introduction to Philadelphia. Blount was stuffed for a 2-yard loss on the game's first play, and it wasn't the only time he went backwards. Pederson wanted to establish the run more Thursday than he did last week, but the lanes were slow to open with Peters out of the lineup, and Blount was slow to find them.

Blount lost yardage on two of five carries, and he finished with five carries for 8 yards. He also caught two passes for 15 yards and fumbled on his second reception, halting the first-team offense's only productive drive.

The rest of the time the starters were on the field, Wentz appeared under duress. He was sacked once, scrambled from pressure for a  1-yard gain another time, and will now need a strong third preseason game to enter the regular season with momentum. Wentz finished 6 of 9 for 56 yards in his first game without Jordan Matthews, but it was Peters whom Wentz might have missed the most.

The good news for those willing tolerate preseason football at the Linc was they saw a swarming Eagles defense that has now forced three turnovers on six preseason drives and has not yet allowed points.

"The pass rush was there tonight and disrupting some of the timing offensively," Pederson said. "Our guys were in position to make plays. …It's great to see our defense come up with takeaways and put the offense in good situations."

On their third play Thursday, defensive coordinator Jim Schwartz sent safety Rodney McLeod on a blitz. Schwartz is selective about when he chooses to send extra pressure, and the Bills didn't account for the sprinting McLeod. He zipped into the backfield and deflected Tyrod Taylor's pass, which Mychal Kendricks caught for an interception in the red zone.

It was Kendricks' second interception in two games. Kendricks' playing time took a dramatic dip last season because Schwartz kept him on the field only in base packages, and Kendricks requested a trade after the season. He's still with the Eagles, still in the same role, but he is playing at a high level.

Kendricks, who finished with one sack, even applied pressure for the Eagles' next interception. It came on the first play of the defense's fourth drive, when Taylor rolled to his right and tried to find Anquan Boldin. Darby, who has practiced against Taylor for the last two years, jumped in front of the pass and returned it 48 yards.  The interception offered redemption for Darby against the team that traded him after two seasons, and offered a favorable first impression for his new fans.

"They were running a lot of routes that looked similar," Darby said, "so I was just being patient with everything and cutting them off."

The Eagles held a 3-0 lead when most of their starting offense and starting defense left the field. The reserves took over from there, with rookie Derek Barnett recording his third sack in two games. Matt McGloin, who was the No. 2 quarterback with Nick Foles out, went 12 of 20 for 131 yards and one interception. Running back Corey Clement, a Glassboro native, rushed for a touchdown in his first home game.

The reserves will receive considerable time in the preseason finale in two weeks. Next week's third game will offer more of a chance for the starters. The defense simply needs to continue what it showed Thursday, but the offense must show improvement in what's likely to be its final tune-up before the Sept. 10 season opener against Washington.

"The minute we begin to game-plan and we give our starters the whole week of practice," Pederson said, "things do become different at that point."