The sweltering heat on Sunday made some diehard U2 fans question — at least briefly — the extent of their loyalty to the Irish rock band.

The dilemma: melting under a blazing sun all day to snag a highly coveted spot up close to the stage or coming later and viewing the concert from farther away.

"I thought twice about it because the Chicago show was so hot, too," said Twila Peitz of Iowa.

For the early birds, general admission tickets meant standing for hours on a part-aluminum floor, but the diehards were up to the challenge.

"We love general admission," said Peitz's friend, Nat Ebbing of St. Charles. "It's taxing on the body, but once we're up there, it's worth it."

They were among the hundreds of sweaty fans who began lining up outside Busch Stadium before 5 a.m. Sunday for the biggest concert in St. Louis history. They weren't allowed in the stadium until after 4:30 p.m. As midafternoon temperatures rose into the mid-90s, many folks cooled off under two misting stations that were set up nearby. They also could refill water bottles at a first aid station.

Many of the concertgoers came with umbrellas, coolers of water and canopies to stay out of the sun. Most of them even had closed-toe shoes, having been warned that flip-flops would be potentially hazardous on the burning hot floor.

Ebbing even brought a pack of deodorant with him to share with the folks around him, figuring many of them would need to freshen up after spending eight-plus hours in the heat.

But by midmorning, the Old Spice had liquefied. It got all over his hands when he opened it.

"It was like wax," he said. "But I smell very fresh and clean. Very spicy."

While some braved the heat, many fans stayed home until closer to the start of the 7 p.m. show.

Mike Ball, director of event operations and guest services for Busch Stadium, said his staff was preparing for as many as 2,500 to 3,000 fans to line up. But by about noon, only about 500 fans were in line.

"I think it will be a late crowd" because of the heat, he said. More than 50,000 people attended the show.

The St. Louis region has been under an excessive heat warning since Saturday. The National Weather Service extended the warning through 7 p.m. Friday and has said that heat index values could reach between 105 and 115 degrees. A high of 100 degrees is predicted for Tuesday through Friday.

St. Louis Mayor Francis Slay went door to door in the city's Dutchtown neighborhood on Sunday to warn residents to take precautions this week in the extreme heat.

Cool Down St. Louis, an energy-assistance charity, made an appeal to congregations on Sunday for parishioners to check all week on elderly and disabled members of their community.

Concert coordinators didn't want people to start lining up for the concert until 7 a.m. Sunday. But Kirsten Nielsen, a St. Louis native who now lives in Dublin, and a few others began an unofficial line at 10 a.m. Friday. By Sunday, she had sunburned legs.

Nielsen recalled that a U2 show in Dublin she attended in 2009 was cold and rainy.

"Now I'm kind of wishing for that," she said.