NEW YORK — In the middle of September, with the temperature in the upper 80s and the heat of battle over 100, Angelique Kerber did a snow angel.Laying on her back on the baseline of Arthur Ashe Stadium, limbs akimbo, Kerber was in the first throes of emotion after winning the U.S. Open on Saturday. Karolina Pliskova's shot sailed long and Kerber's career, already at an all-time high, sailed to its apex. That's when she dropped to her back in celebration.With a 6-3, 4-6, 6-4 victory over the surprising Pliskova, Kerber bookended the Gram Slam season with her second major of the year. When Williams was beaten by Pliskova in the semifinals, it assured that No. 2 Kerber would displace Williams as No. 1 in the world, a ranking she has held for 186 weeks."It's just incredible what I did this year," Kerber said. "I'm really so happy and so proud about everything what's happened now about my team, about my game and about my improvement."When I was a kid, I was always dreaming to one day be the No. 1 player … to win Grand Slams. I mean, all the dreams came true this year." Never a Grand Slam finalist before 2016, Kerber beat Williams for the Australian Open title in January, then was runnerup to her at Wimbledon. Adding the championship at Flushing Meadows was further proof that all of the changes Kerber has made are paying off. The better fitness, via extra time in the gym and longer, more intense practice sessions; an improved serve and a new willingness to attack during points, rather than mainly counter-punching, via instruction from coach Torben Beltz; a more positive attitude on court, via help from a mental coach. "Of course, now everybody will try to beat me and have nothing to lose," Kerber said. "I will try to take this challenge." On Saturday, Kerber trailed by a break at 3-1 in the third set before coming back against the 10th-seeded Pliskova, who hadn't been past the third round at a major until this tournament. Kerber is the first woman from Germany to win the U.S. Open — and the first to get to No. 1 — since her idol and mentor, Steffi Graf, who got in touch via text message before the final. It was Pliskova of the Czech Republic who guaranteed Kerber's ascension in the rankings by beating Williams in the semifinals, ending her streak of 186 that equaled Graf's mark. Kerber, who collected $3.5 million in prize money Saturday, lost to Pliskova the last time they met, just three weeks ago in the final of a hard-court tournament in Cincinnati. But at the outset of this final, it was Kerber who was in charge. Her defense is exemplary, scrambling along the baseline to put her racket on seemingly every ball, crouching so low that her knees would come close to scraping the ground. "With Angie, you cannot wait for mistakes," Pliskova said. "She doesn't give you anything."I mean, definitely, I would say now that she deserves to be No. 1. And after years (when) Serena was there, I think it's a nice change."