Clearly the class of the field, Hoff survived a poor start in the 200-meter freestyle to set an American record - her second in two days - and then came back two hours later to win the 400-meter individual medley, bringing her total to four gold medals with two events to go.
Phelps started the morning with a win in the 200-meter freestyle final and felt good about his swim. So before the 400 IM finals, Phelps and Hoff agreed to a friendly wager on the pool deck: $20 went to whomever got closer to their world record. Hoff, cruised, winning in 4 minutes, 34.53 seconds, a little less than two seconds off her best.
"I guess I have to go 4:07," said Phelps, raising an eyebrow when his coach, Bob Bowman, showed him Hoff's mark. It didn't happen. In fact, he didn't even come close. Phelps was sluggish for nearly the entire race, and though he was able to hold on for the win, his time (4:14.08) left him visibly annoyed at the finish line. "I was happy with the 200 free this morning, not very happy with the  IM," he said. "Just a lot of things I can change."
Phelps said he has to be in better shape and improve his recovery time between events.
"I have to go back into being able to swim back-to-back events and be able to swim them well," he said. "Bob and I know what we have to do in training."
Bowman, though, said he didn't mind watching Phelps struggle a bit. "He'll get more out of that than anything he's done in this meet," Bowman said.
Even Hoff knew better than to tease the grumpy Phelps about his debt, instead needling Bowman about when she would get to collect her loot.
"I don't think I'm supposed to talk about that," a sheepish Hoff said afterward.
Seal-sleek in her black one-piece Speedo suit, Hoff broke late from the blocks in the 200 free and had to chase down the leaders, Natalie Coughlin - the U.S. record holder until yesterday - and Kara Lynn Joyce.
"I popped up and looked all around and I was, like, 'OK, I'm behind and it's not even the 25 [meter mark],' " Hoff said. "I know Natalie and Kara have good kick-outs and are strong sprinters, so ... my game plan was to relax in the first 50 and then really build into the 100."
By the first turn, the Towson swimmer had a half-length lead and built on that to win in 1:56.08, a second better than her personal best and 0.35 of a second faster than Coughlin's former American record. Hoff's time is the third fastest in the world behind France's Laure Manaudou (1:55.52) and Germany's Annika Liebs (1:55.68), both set last year at the FINA World Championships.
Hoff had set the American record in the 400 free Saturday. In the 400 IM, she battled through the butterfly and backstroke against Zimbabwe's Kirsty Coventry, winner of three Olympic medals in 2004, before pulling away in the breaststroke and putting away the race in the freestyle, the final 100 meters.
Although she has dominated the meet, Hoff dismissed any attempt to label her as the best American woman leading up to the selection of the Olympic swimming team in early July.
"I'm just excited to be confident going into the next five or six months [of] training and getting ready for [Olympic] trials," she said.
But Phelps praised his former teammate at the North Baltimore Aquatic Club.
"Last year, she really came into her own," Phelps said. "She was able to do what she was capable of doing, and I think she's a very, very talented swimmer and a hard worker and we're all starting to see that now.
"It's not only us two. Our club, NBAC, has always had a very strong swimming team and a tradition for excellence. I have no idea what they put in the water, but obviously it's something good."
Hoff admitted to feeling more nervous as the wins pile up at this meet and said her coach, Paul Yetter, noticed it before yesterday's finals.
"I felt I kind of set the bar high for myself," she said, referring to her first two gold medals Saturday. "[Yetter] said, 'Relax, just relax and have fun with it. You're having a great meet. Be relaxed and you'll swim fast.' "
Also yesterday, Coughlin, a five-time Olympic medal winner, set a world record in the 100-meter backstroke during a preliminary race. She finished in 59.21 seconds, lowering her record by 0.23 of a second.