What to watch: The anticipated clash between rivals Ryan Lochte and Michael Phelps could be the race of the meet. Lochte, 31, is the world-record holder with a 1:54.00 from 2011 while Phelps, who turned 31 on Thursday, is the three-time defending Olympic champion in the event. Phelps also will be navigating the preliminaries and likely the semifinals of the 100 butterfly. The women’s 100 free final will be critical because of the relay spots and the potential insight on Katie Ledecky’s range. The U.S. women were third in the 400 free relay at the FINA World Championships last summer, so fastest times would be a welcomed sight for the federation.