It takes more than caffeine to beat Elina Svitolina, though.

Williams had a resurgence after some coffee was sent her way after dropping the first set against the No. 5 seed, but Svitolina charged back and eventually beat Williams 6-4, 6-4 in a second-round match at the US Open.

"It was a lot of positives for me today," Williams said. "I served well and I played well. She played well. There's a lot for me to build on from there. I'm excited to get to my next matches and sad it had to end early here."

The cup of coffee was delivered from Williams' team in the stands to a ballboy, who tried to bring it to Williams. But she walked off to the court between sets before he could get it to her, so he eventually dropped it off next to her seat.

Williams then came back to take a 3-0 lead to start the second. But having to save four break points for a tough hold in that third game seemed to take something out of the 39-year-old Williams, as Svitolina came right back to take five straight games for a 5-3 lead.

"I had to stay very focused," Svitolina said. "I was expecting that she would raise her level."

Williams then fought off five match points in a 22-point game to hold her serve before Svitolina eventually ended it on her sixth chance, improving to 13-3 in Grand Slam matches this season.

"She always plays extremely well against me," Williams said. "You know, she can keep that form up and she's got a lot of great things ahead of her. I think there are probably a lot of matches that are winnable for her that she hasn't been able to win. But against me, she plays extremely well."

Venus Williams isn't happy about losing a point to Elina Svitolina. Associated Press

Third-seeded Karolina Pliskova advanced easily Wednesday, dispatching her second-round opponent in a little over an hour.

Unlike top seed Naomi Osaka and No. 2 Ash Barty, who have been pushed to three sets, Pliskova rolled over qualifier Mariam Bolkvadze 6-1, 6-4, and has yet to drop a set.

Pliskova, a finalist at Flushing Meadows in 2016, served extremely well, blasting nine aces and winning 90% of her first-serve points.

Hers was the first match of this year's tournament played under the roof at Arthur Ashe Stadium because of a light rain that's been falling all day.

Rain has forced the postponement of all U.S. Open matches Wednesday except those in the two main show courts with retractable roofs.

The decision was made late in the afternoon after players attempted to start matches on uncovered courts during a break in the weather, only to be chased off by showers once again. And there was a 70 percent of more rain for later Wednesday.

Fans, of course, were still able to see tennis in Arthur Ashe Stadium and Louis Armstrong Stadium, where the roofs were closed early Wednesday in anticipation of the drizzly rain that fell off and on for most of the day.

The other good news: Sunny skies and temperatures in the 80s are in the forecast for the next two days.