Harbaugh turned out to be an excellent special teams coordinator for the Eagles before going to Baltimore, where he became the first coach in NFL history to lead a team to playoff wins in his first four seasons.
Harbaugh returns to Philadelphia to face his old boss and his old team when the Ravens (1-0) play the Eagles (1-0) on Sunday.
"It's special," Harbaugh said. "It really doesn't hit you until you get there. Then, all of a sudden, your emotions flood up on you. That happened in the preseason last year when we played there. I assume this year will be the same, or even more intense."
Harbaugh was a first-year assistant coach under Ray Rhodes when the Eagles went 3-13 in 1998. Rhodes was fired after that season and replaced by Reid, who brought in an almost entirely new staff.
But Harbaugh stayed.
"He's a football coach, he's a teacher, he's intelligent and a hard worker," Reid said. "He's tough and good with people. Those are qualities that you need to advance as you move up the coaching ladder."
Harbaugh coached special teams for nine seasons and was in charge of the secondary his last year in Philadelphia. He then made the leap to head coach when Ravens general manager Ozzie Newsome hired him to replace Brian Billick in 2008.
All he's done is win. Harbaugh has led the Ravens to the second-most wins (50) in that span, including playoffs.
"Ozzie gave him an opportunity where a lot of people would ignore a special teams coach," Reid said. "I think the special teams coach has to deal with both sides of the football and as many people as a head coach does as far as it comes to dealing with the football team. Then he had the experience of dealing with the media. Their job is a little underrated in my eyes, and then he had the opportunity to move over to the defensive side for one quick shot there."
Harbaugh and Reid built a close bond during their time together. When Garrett Reid, the oldest son of Andy and Tammy Reid, died during training camp, Harbaugh was one of several coaches who traveled to attend the funeral.
"I've got a lot of respect for Andy," Harbaugh said. "I've got a lot of love for his family."
They'll put friendship aside for a few hours Sunday.
The Ravens and Eagles took different paths to victory in their openers. Philadelphia needed a late touchdown to beat Cleveland 17-16 and avoid a major upset. Baltimore, on the other hand, dominated Cincinnati 44-13 in front of a national TV audience Monday night.
Michael Vick threw four interceptions before leading the Eagles on a winning 91-yard drive in the final minutes. Meanwhile, Joe Flacco was the AFC's offensive player of the week after a sterling performance. He was 21 of 29 for 299 yards and two touchdowns.
The visit to Philadelphia is even more of a homecoming for Flacco than Harbaugh. The quarterback grew up in nearby Haddon Township, N.J.
"I grew up around all Eagles fans, and they're a pretty passionate group," Flacco said. "Who knows who my buddies will be rooting for? Hopefully they'll have a little compassion for me."
Flacco and an offense that features two-time Pro Bowl running back Ray Rice presents problems for defenses because they often run without a huddle. Flacco led to 430 total yards against a Bengals defense that ranked 10th in the league last season.
"You have to be poised with the no-huddle," Eagles linebacker DeMeco Ryans said. "You can't panic. That's the biggest thing they want you to do is panic and change personnel and match up with what they're doing. You can't panic. You just have to be calm, play solid, and stop them on first and second downs to get them at third-and-long."
The Eagles scored both of their touchdowns against the Browns in the two-minute drill, but Reid doesn't plan to use it.
"That's not our primary thing," he said.
Vick already poses enough challenges for defenses with his speed and escapability. He just needs to limit his turnovers.
"We understand who we're playing," Ravens linebacker Ray Lewis said. "We understand what Michael Vick is going to give us when we come to Philly, so we won't let what happened last week in Cleveland ever fool us. You have to come play him as who he is. You come in and play the same guy that you know is that spectacular guy with the football, that can throw the ball 80 yards, that can run the ball out of the pocket, that can make you miss, that can make incredible plays out of the pocket. I think that's what you have to prepare for."
The last time these teams met in Baltimore in 2008 was a turning-point game for the Eagles. Donovan McNabb was benched at halftime for the first time in his career in what ended up being a blowout loss. But McNabb rebounded to lead the Eagles to an improbable playoff berth, two road playoff wins and a fifth trip to the NFC championship game in eight years.
Vick doesn't need to get benched to understand he must improve if the Eagles are going to contend this season.
"I shook off the rust last week and I'm ready to get back out against Baltimore," Vick said. "The thing that I can tell you is that we will progress and get better as the season goes on."