In the first race of the night, Canada's Emily Overholt appeared to win the women's 400 IM in Pan Am-record time before judges ruled that she failed to touch the wall with both hands at the same time on one of her breaststroke turns.
It's a rare call, but on Thursday it would be made twice.
In the men's 400 IM, Brazil's Thiago Periera thought he had won his third straight Pan Am title, but was disqualified for the same reason as Overholt.
For Periera, the gold would have been his 22nd Pan Am medal, tying the all-time record.
Disqualifications happen in swimming, but it's uncommon for them to fall on winners in back-to-back gold-medal races. It's even stranger to see it happen for the same reason.
Non-simultaneous touching is hardly ever called, with the most common disqualifications coming from swimmers leaving the starting blocks early or taking more than 15m to start their strokes.
The rash of DQs extends back to Wednesday night, when the U.S. team was disqualified from the men's 4x200m relay because their leadoff swimmer, Michael Wiess, had taped his fingers together due to an earlier injury. The Americans, though, appealed the call and the DQ was overturned.
Canada and Brazil were hoping for the same outcome as both teams appealed the calls against them on Thursday night, but the appeals were reportedly rejected.