Team GB's Michael Rock and James Antony have bowed out of the men's 100m butterfly at London 2012.
The former swam in the fourth heat, and struggled to compete with pace-setters Evgeny Korotyshkin of Russia and Tyler Mcgill of the United States.
He came in seventh in his group with a time of 52.56s, ranking him in an overall 24th place.
Antony was drawn in a tough heat alongside Michael Phelps. The Baltimore Bullet powered through the heat to finish in first with a time of 51.72s. Antony trailed the rest with a time of 53.25s.
Phelps faces stuff competition in tonight's semi-finals from South African Chad le Clos, who has already beaten him to gold in the 200m butterfly.
Le Clos won his heat and was the fastest qualifier with a time of 51.54s.
