US Open, Day 4: Halep marches under roof after rain

Romanian fifth seed Simona Halep advanced to the third round of the U.S. Open with a 6-3 6-4 win over Lucie Safarova on Thursday in the first full match played under a closed roof at Arthur Ashe Stadium.

The $150 million retractable roof was installed ahead of this year's tournament and guaranteed there would be at least some action on a muggy and overcast Day Four at the year's final grand slam.

"It was a little bit (of an adjustment)," Halep said about playing under the roof. "But I had the chance to warm up in the morning before the match.

"I don't want to say anything bad because it wasn't bad. Had a nice feeling.

"It was a great experience to be there. I didn't have to wait for the rain, so that's a good thing," she said. 

Czech Republic's Karolina Pliskova defeated Montserrat Gonzalez of Paraguay 6-1 7-5 in another match. 

Heavy rain forced play to be suspended at Flushing Meadows except for the closed roof at Arthur Ashe Stadium.