Mary-Kate and Ashley Olsen Celebrate Their Birthdays With an Olympics-Themed Party

— -- Mary-Kate and Ashley Olsen traded their couture for cutoffs to celebrate their 29th birthdays.

The fashion designers toasted their big day -- June 13 -- with an Olympics-themed bash in the Hamptons.

"Happy Birthday my beautiful MK. You will always be a winner in my book.. Except today," wrote one of their friends, Jared Seligman. "#olsenolympics #werenumber1"

The Olsens kicked off their big weekend with ice cream sundaes and passed out Team Mary-Kate or Team Ashley shirts to their pals. In keeping with their birthday, the number "29" appeared on the back.

Among the games played were an obstacle course and a dunk tank and, in the end, Team Ashley was victorious.

"Happy Birthday #TeamMK #OlsenOlympics"

"Champions ???? #teamashley #olsenolympics #twinning #sorrymk"

"Happy Birthday my beautiful MK. You will always be a winner in my book.. Except today ???? #olsenolympics #werenumber1"

"#OlsenOlympics"

"Got #danconnor in the dunk tank, first try ?? #olsenolympics"

"Let the games begin"