Pella raised his level in set number three, serving well and earning a break in game seven when they returned to the court after the first delay, but that was the last game we saw for today.
"Everyone had told me I was going to love it and all that", she said. After dropping her first set to Romania's Alexandra Gulgheru, No. 9-seeded Williams bounced back strong to take two decisive back-to-back sets and move on.
No such problems for Federer, who won 35 straight points on his serve on route to beating Lukas Lacko of Slovakia 6-4, 6-4, 6-1.
The third set was one-way traffic as Federer killed the contest with a ferocious forehand after 90 minutes of brilliance.
But the American, the runner-up at Wimbledon a year ago, then won seven games in a row.
Federer again opted to skip the clay-court season to prepare himself for Wimbledon and will take some stopping as he goes in search of a 99th tournament triumph at the All England Club. "Sometimes your serve matches up better against certain players". "From my end I'm very happy".
Outside of the Williams sisters, who have 12 Wimbledon titles between them, Keys is viewed as the next likely United States champion at the All England Club.
Williams was almost as good, losing just five of 32 points on her first serve in a 6-1, 6-4 win over Viktoriya Tomova.
It was another dominant display by the eight-time champion, who lost just nine of 61 points on his serve in total and broke Lacko five times, including with a forehand victor to close out the match. "I'm happy how I am hitting the ball, good concentration on my service games and able to mix it up with some slices".
French 18th seed Lucas Pouille was cast aside on Wednesday by Austrian qualifier Dennis Novak, ranked 152 places below him.
Serena Williams of the United States returns to Viktoriya Tomova of Bulgaria during their third round match at Wimbledon on Wednesday.
Even ultimate warrior Williams, who was unable to defend her 2016 Wimbledon title previous year because she was pregnant, applauded a couple of her opponent's winners late in the second set before completing victory in 66 minutes.