Pettersen, the Norwegian star ranked sixth in the world, shot a 4-under 68 at Blackwolf Run on Friday and moved to 5 under for the tournament. But Wie was even better, carding a 6-under 66 to move to 4 under and put herself in position to break out of a season-long slump.
Wie was tied with Cristie Kerr, the 2007 Open winner, one stroke off the lead.
Pettersen was playing in the group directly behind Wie, giving her a pretty good view of what turned out to be an impressive display of accurate approach shots and made putts.
"She was fist-pumping, every putt she looked at," Pettersen said.
Wie said she doesn't spend much time thinking about the attention she received as a high profile child prodigy in the early 2000s, or whether some fans had written her off since then.
"I don't know if anyone gave up on me or not," Wie said. "I'm sure some did and some didn't. But I never gave up on myself, and today was a good reminder to myself that I can do (it) and I still have it."
Kerr, who was tied for the first-round lead at 3 under with Lizette Salas and Brittany Lincicome, had a 71.
"I always draw on that experience, of course, but it's hard to predict what's an advantage and what's not an advantage," Kerr said of her previous Open win. "You just don't know."
Sandra Gal, Inbee Park and Vicky Hurst each shot 70 to reach 3 under.
Salas, a 22-year-old recent Southern California graduate, had a 73 to drop to 2 under. Mika Miyazato also was 2 under after a 71.
Lincicome had a miserable day, shooting an 80 to fall to 5 over.
"I did nothing right today," Lincicome said. "I couldn't drive the ball. I couldn't do anything right. I couldn't putt."
Lexi Thompson, 17, shot a 73 to top the group at 1 under.
Top-ranked Yani Tseng was 2 over after a 72.
Second-ranked Stacy Lewis recovered from a first-round 77 to shoot a 69 on Friday, putting her 2 over. Third-ranked Ai Miyazato, the winner last week in Arkansas, was even par after a 74.
Defending champion So Yeon Ryu shot a 71 and was 1 over.
Se Ri Pak, the Open winner at Blackwolf Run in 1998, also was 1 over after a 73.
Seeing Wie's name near the top of the leaderboard will ring a bell with casual golf fans, even if they haven't heard from her in a while.
Wie was 12 years old when she qualified for an LPGA Tour event in 2002 -- making her at the time the youngest player ever to do so. She went on to compete in a handful of men's tournaments, but never turned her early stardom into consistent success. She has two career LPGA Tour victories.
Now she's 22 years old, a recent Stanford graduate -- and, at least before Friday, struggling on the course.
Wie has missed six of eight cuts this season, although she says she has been feeling better about her game.
"The last couple of weeks it started to feel good," Wie said. "Things were coming. My scores weren't showing up as well. But it's a work in progress. Still a long way to go."
And Wie knows she's a long way from a potential victory Sunday, but is excited to have something to shoot for beyond simply making the cut.
"The fact that you're in contention to have a chance to win the U.S. Open is a big deal," Wie said. "I'm so grateful I have that chance right now. I'm really looking forward to seeing the crowds tomorrow and experiencing it all again."
Pettersen said Wie should be given some space to find her game at her own pace.
"I think you should give her a break," Pettersen said. "She just graduated, four years in college. That's pretty impressive to do that on the sideline of trying to compete out here. So now it's obviously a little different world for her. Now it's all about golf, and she has to kind of find her schedule, how to kind of work it out the best way for her."
Pettersen, meanwhile, believes her own game is in good shape.
"My game is very solid," Pettersen said. "My ball striking is good. My short game is good. And my putting has been really good so far."
Her day got off to a hectic start when she overslept and had to rush to make her tee time, skipping breakfast.
"For me breakfast is kind of my most important meal," Pettersen said. "I didn't really have time. I thought it was more important to get stretched and loosened up. Even though it's hot. It's fine. Sometimes that's a good thing. You don't have time to think about stuff."
The intense heat and humidity players and fans dealt with in Thursday's first round eased only slightly on Friday. The final two days of the tournament are expected to be more pleasant.
"Hopefully we're done with the two hot days, and they're all calling for a cooler weekend," Pettersen said. "Which I'm all for. It's been two really hot days."
Cheyenne Woods, the niece of Tiger Woods, missed the 5-over cut after a 78 on Friday. She finished at 9-over.