Michael Phelps will be top seed in the men's 100 metres freestyle final after qualifying equal fastest.

Beaten by world record holder and American Olympic team-mate Aaron Peirsol in the 100m backstroke final on Saturday night, Phelps resumed his search for a third gold medal of the meet at the Mecklenburg County Aquatic Centre in the 12th of 13 100m free heats.

The eight-time Beijing Olympic gold medalist, who won the 200m free and the 100m butterfly finals on Friday night, clocked 49.5 seconds to win his heat, a time matched in the final preliminary by fellow American Ricky Berens.

Cullen Jones, another Beijing team-mate, finished second behind Berens and third fastest overall in 49.75, edging 50m free world record holder Frederick Bousquet of France (49.81) in the final heat.

Bryan Lundquist, Tyler McGill, Davis Tarwater and Bobby Savulich round out a strong field for the final race of the meet, although another main rival, Ryan Lochte, did not start.

Phelps was returning to competition for the first time since his Beijing heroics but also having served a three-month suspension following the publication of photographs appearing to show him using equipment associated with marijuana use.

The 23-year-old had also reached the 50m freestyle final on Saturday night but chose not to compete.

Durham's Stephanie Proud, swimming for the University of Florida's Gator Swim Club, qualified fastest for Sunday night's women's 200m backstroke final in 2:11.40.

American Mary Descenza was next fastest, clocking 2:13.46 to beat 16-year-old US Olympian Elizabeth Beisel (2:13.90), the event top seed, in their heat.

Marco Loughran of Swim Wales followed his B final victory in the 100m backstroke on Saturday night by making the A final in the men's 200m backstroke by qualifying second fastest.

Loughran, 20, clocked 2:02.28 slower only than Tyler Clary (1:59.14) with Peirsol, the event's top seed, third fastest from the heats, swimming well within himself to clock 2:02.48.

Peirsol's prospects for a second gold medal of the meet were enhanced considerably when chief rival Lochte also scratched from those heats.

Loughran's club-mate Joseph Canlan-Shaw will contest the C final after clocking 2:09.29.

Shoreham's Gemma Spofforth was in unfamiliar territory in the 200m individual medley preliminaries but qualified for Sunday night's C final with the 18th fastest time of 2:22.46 and also made the 200m backstroke C final in 2:21.15

Georgia Holderness of Swim Wales swam 58.83 in the 100m free preliminaries but did not progress to the evening session.