A day after kicking off the 2015 U.S. Open, several stars will round out the opening round on Tuesday.
Serena Williams, Novak Djokovic and Rafael Nadal commenced New York's festivities with Round 1 victories. Yet a pair of top contenders suffered early exits, placing all other premier players on upset alert.
Kei Nishikori, a finalist last year and the tournament's No. 4 seed, lost to Benoit Paire in five sets. On the other side, Dominika Cibulkova ousted No. 7 Ana Ivanovic. A window of uncertainty has now opened in Queens, so none of Tuesday's top contestants can coast through their initial draw.
|U.S. Open Tuesday TV Coverage|
|First Round||11 a.m. - 11 p.m.||ESPN3||Watch ESPN|
|First Round||1 p.m. - 7 p.m.||ESPN||Watch ESPN|
|Primetime at the U.S. Open: First Round||7 p.m. - 11 p.m.||ESPN||Watch ESPN|
No. 2 Simona Halep vs. Marina Erakovic
Although seeded No. 2, galaxies separate Simona Halep from Serena Williams. The two recently met in Cincinnati's Western & Southern Open, where the 23-year-old Romanian gave the favorite all she could handle in two tightly contested sets.
Per WTATennis.com, she is viewing the loss as a learning experience if their paths cross again.
"In Cincinnati I didn't believe enough that I could beat her and win the match," Halep said during her pre-tournament media in New York. "I have to improve this for next time if I play her here. I have to just not think about the fact that I'm playing Serena, and just concentrate on winning the match."
Each competitor has a long way to go before setting up a finals bout. Halep, who has never advanced past the fourth round of the U.S. Open, suffered a Round 1 Wimbledon defeat after getting eliminated during her second French Open draw.
The No. 99-ranked Marina Erakovic sports a career 14-23 record in all four majors, going 1-5 at the USTA Billie Jean King National Tennis Center. Don't expect another early exit from Halep after rebounding in Cincinnati.
Pick: Halep in straight sets
No. 2 Roger Federer vs. Leonardo Mayer
Roger Federer has endured a three-year title drought while seeking his 18th Grand Slam title, but the veteran has hardly fallen off the map. Since capturing the Wimbledon crown in 2012, he has made two finals, both at All England Club, and three additional semifinals.
The 34-year-old icon also cemented a No. 2 seed by besting Novak Djokovic in the Western & Southern Open final. After falling to Federer, the No. 1-ranked star offered a glowing review of his rival to ESPN.com's Peter Bodo.
"He's playing some of the best tennis of his life," Djokovic said during Arthur Ashe Kids' Day on Saturday. "Many people did talk about his career coming to an end after that season  that was below his standard, but he came back stronger."
Federer draws a tough Round 1 opponent in Leonardo Mayer, unseeded despite his No. 34 world rank. Tennis View Magazine's Nick Nemeroff noted both competitors' poor fortune seeing one another so early in the bracket:
This marks their second meeting, with the Swiss star grinding out a 7-5, 3-6, 7-6 (7) victory at the Shanghai ATP Masters last year. Federer won't cruise to an easy win against the 28-year-old underdog, but he'll maintain his top form to kick off a deep run.
Pick: Federer in four sets