Coco Gauff, a two-time Grand Slam champion, made a strong return to the US Open with a revitalized serve that powered her to a 6-3, 6-4 victory over Turkey's Zeynep Sonmez in the first round. Gauff started the match with a dominant hold to love, setting the tone for a confident and controlled performance. Her improved serve, which has become a key part of her game, allowed her to recover quickly when Sonmez threatened to take the second set. Gauff, seeded fourth at Flushing Meadows, acknowledged the noticeable improvement in her play compared to last year. "Now it's like I can look back a year and think, 'Oh, wow, it's a big difference,'” she said. Gauff made a significant change to her team last year, bringing in biomechanics expert Gavin MacMillan, who had previously helped four-time major winner Aryna Sabalenka improve her serve. This decision came after Gauff struggled with a high number of double faults at the Cincinnati Open. However, adjusting her technique ahead of the US Open, where the pressure is intense, proved challenging. Gauff was eliminated in the fourth round last year and admitted she felt the weight of expectations. “Obviously last year I knew all the eyes were going to be on the serve,” she said. “Gavin is so great at what he does, I felt a lot of pressure to prove that. It didn’t really show within the first two weeks, which is normal.” Gauff’s serve has since become a more reliable weapon, even though she still occasionally double faults. MacMillan's advice—such as keeping the wrist straighter and improving the toss—has helped her serve with greater accuracy and consistency. This transformation was evident during her Cincinnati Open title run earlier this month, where analysis showed Gauff was hitting her serves closer to the line while maintaining their speed. These improvements have given her the confidence to take risks and go for aces more frequently. Gauff's new approach was immediately apparent in her match against Sonmez. In the opening game, she hit a 112mph ace down the middle, followed by an unreturned first serve and another ace, holding serve in under 90 seconds. Sonmez struggled to keep the ball in play whenever Gauff landed a first serve, with Gauff winning 93% of those points. Although Sonmez fought back to level the second set at 2-2 and had three break points, Gauff’s precision—exemplified by a wide ace and a 115mph unreturned first serve—helped her hold on. This resilience set the stage for Gauff to break for a 4-3 lead and secure the match with a confident service game. Gauff will now face either Spain's Paula Badosa or Australia's Daria Kasatkina in the second round.