NEW YORK, Sept 4 (Reuters) - Fourth seeded Czech Karolina Pliskova rocketed 20 aces past third-round foe Ajla Tomljanovic to win 6-3 6-2 on Saturday, keeping her bid for a maiden major title on track at the U.S. Open. The Wimbledon runner-up had 20 winners in the first set and fended off all five break point opportunities as a handful of costly errors from Tomljanovic, including a double fault in the sixth game to hand Pliskova the break, hampered the Australian"s efforts. Pliskova didn"t drop a single first-serve point in the second set, closing out the affair in an hour and 11 minutes at the Flushing Meadows Grandstand with a trio of aces in the final game. Pliskova, who dug out a tense, three-set match over American Amanda Anisimova in the second round, next faces either Varvara Gracheva or Anastasia Pavlyuchenkova, both from Russia.