Open Extended ReactionsNEW YORK -- An additional 13 teams, one featuring Venus Williams and some comprised of married couples, have entered the US Open mixed doubles championship. Williams is partnering with Alexander Bublik for the tournament that was overhauled last year, with a $1 million prize to the winning team, in an effort to get top singles players to compete. Top-ranked Aryna Sabalenka and 24-time Grand Slam singles champion Novak Djokovic headlined the initial list of 16 teams who entered. That means Sabalenka, the two-time defending US Open women's champion, and Djokovic, still ranked No. Errani and Vavassori are the two-time defending US Open champions.