NEW YORK (Reuters) - Caroline Wozniacki used her aggressive groundstroke game to near perfection on Tuesday to reach the semi-finals of the U.S. Open with a 6-0 6-1 victory over Italy's Sara Errani.The 10th-seeded Dane beat 13th-seeded Errani at her own strategy, engaging in long baseline rallies but using superior power to open the court and find lanes for blasting home winners.