SANTA CLARA, Calif. (AP) — Chip Kelly and Jim Harbaugh have been fierce competitors in college when Oregon and Stanford battled for West Coast supremacy.

They have been long-distance admirers of the way each can create mismatches through formations and play design. They have even been collaborators who have traded ideas on football philosophy.

The relationship that began when both arrived in the Pac-10 seven years ago reaches a new chapter Sunday when they meet for the first time as NFL head coaches when Kelly and the Philadelphia Eagles (3-0) take on Harbaugh's 49ers (1-2).

While their teams look different on the surface with Kelly using a fast-paced, spread attack that utilizes the entire width of the field compared to Harbaugh's preferred power, running system, the fundamentals are quite similar.

"From an offensive standpoint, both teams start with the run game," said Eagles tight end Zack Ertz, who played for Harbaugh at Stanford. "They use that to set up everything else."

Kelly is known as an innovator, who bucks tradition when it comes to practices, nutrition and most of all offensive philosophy.

After battling with Kelly's Oregon teams in college, Harbaugh sent offensive coordinator Greg Roman to Eugene, Oregon, to learn more about Kelly's offense.

"It's evolved," Harbaugh said. "They've done some great things offensively. I see their fingerprints on the defense as well. You see a progression and consistently good football and great adjustments and sound schematics."

Kelly returned the favor and visited the 49ers in 2012 during an off week for the Ducks in hopes of gleaning some insights unto Harbaugh's approach.

"One thing about Jim, he's won everywhere he's been," Kelly said. "He won when he was a player. He won when he was at the University of San Diego. He won when he was at Stanford. He's obviously been very, very successful with the 49ers. He's a competitor. He's a grinder. He's got a passion for this game, and his teams kind of reflect his personality."

Here are some other things to watch when the 49ers host the Eagles:

TALE OF TWO HALVES: San Francisco and Philadelphia have been mirror opposites so far this season. The Niners have started fast and then wilted in the second half, outscoring opponents 59-16 in the first half only to have it reversed in the second when they have been beaten 52-3. The Eagles, on the other hand, have become the first team to start 3-0 after trailing by at least 10 points in each game. They've done it by outscoring the opponents 74-24 after halftime.

LIMPING LINE: A year after having remarkable stability on the offensive line with five players starting all 17 games, the Eagles line is in shambles early this season. The latest casualty is center Jason Kelce, who had sports hernia surgery this week. With All-Pro left guard Evan Mathis and backup right tackle Allen Barbre already hurt and starting right tackle Lane Johnson serving the final game of his four-game suspension, left tackle Jason Peters is the only player in his usual spot. Left guard Matt Tobin and center David Molk are set to make their first career starts and Dennis Kelly is moving from left guard to right guard, with Todd Herremans moving from right guard to tackle.

FLAG DAY: The 49ers have been done in by their own mistakes early this season, most notably with a league-worst 36 penalties through three games. A barrage of personal fouls did in San Francisco last week when late hits by Dan Skuta and Patrick Willis keyed Arizona's go-ahead drive and calls against Anquan Boldin and Jonathan Martin ended a potential scoring drive that could have given the Niners the lead back.

"We'll address it," Harbaugh said. "We'll work to fix things. There's things that need to be fixed and have great confidence we'll get them fixed."

FANTASTIC FOLES: Philadelphia quarterback Nick Foles is proving last year's breakthrough season was no fluke. Foles, who led the NFL in passer rating a year ago, is tops in yards passing this year with 978 through three games. Foles is looking to join Peyton Manning, Steve Young, Kurt Warner and Drew Brees as the only QBs to open the season with four straight 300-yard passing games.

WHERE'S GORE?: Frank Gore has been the staple of Harbaugh's offense so it has been a bit of a surprise how infrequently he has been used this season. Gore has just 35 carries, including only six last week against Arizona, as the Niners have turned more of the offense over to quarterback Colin Kaepernick.

"Whatever works, I'm with it," Gore said. "If it's passing, it's passing. If it's running, we run it. I'm willing to do whatever it takes to win."

___

AP Pro Football Writer Rob Maaddi in Philadelphia contributed to this story.

___

Online:

AP NFL website: www.pro32.ap.org and www.twitter.com/AP_NFL