The ace bounced off the Court 1 backstop as Williams trotted to the net to bid another foe farewell.
The scoreboard said 127 mph, the fastest women's serve ever recorded at Wimbledon. The scoreboard also had Williams winning 6-1, 7-5 Saturday over qualifier Maria Jose Martinez Sanchez.
It was an upset-filled first week at Wimbledon and a rough one for American tennis, but the nonconformist Williams sisters ignored both trends. Four-time champion Venus and two-time champion Serena won three matches each without dropping a set.
Both advanced to Monday's round of 16, as did No. 2-ranked Rafael Nadal on the men's side.
With No. 1-ranked Ana Ivanovic and No. 2 Maria Sharapova eliminated, and with No. 3 Jelena Jankovic limping to victory Saturday, prospects look good for an all-Williams final next weekend.
"The chances were wonderful from the beginning, from round one," Venus said. "That's how we see it. The more we progress, obviously the closer it gets."
It would be their first meeting in a Grand Slam final since Serena beat Venus for the 2003 Wimbledon title.
Potential pitfalls remain, Jankovic foremost among them. But she hurt her left knee in the first set against 17-year-old Caroline Wozniacki.
Jankovic won 2-6, 6-4, 6-2, finishing the match with her leg heavily wrapped. She planned to have an MRI exam before facing Tamarine Tanasugarn on Monday.
"I don't think it's that bad," Jankovic said. "I hope for the best so that I will be able to play my next match."
Unable to overcome injury was French Open runner-up Dinara Safina, who finished in tears as she lost to Shahar Peer 7-5, 6-7 (4), 8-6. Safina, who required treatment of her thighs during at least two changeovers, cried between points and hit half-speed serves in the final game, then double-faulted on match point.
Alla Kudryavtseva had a successful encore to her upset of Sharapova, reaching the fourth round at a major event for the first time by beating Peng Shuai 6-3, 1-6, 6-4.
With a late start on Centre Court, Nadal barely beat darkness but easily defeated Nicolas Kiefer 7-6 (3), 6-2, 6-3. Runner-up to Roger Federer the past two years, Nadal is trying to become the first man to consecutively win the French Open and Wimbledon since Bjorn Borg in 1980.
On Monday he'll play No. 17-seeded Mikhail Youzhny. In the wake of the worst showing by American men at Wimbledon since 1926, with no one reaching the second week in singles, top-seeded Bob and Mike Bryan advanced to the doubles quarterfinals.
But the U.S. curse extended to Russian Dmitry Tursunov, who lives in California, and German Tommy Haas, who lives in Florida. Both lost.
Tursunov was beaten by Janko Tipsarevic, who upset Andy Roddick in the second round. Haas was defeated by Andy Murray, seeking to become the first British man to win Wimbledon since Fred Perry in 1936.
The marquee men's match Monday will be five-time defending champion Federer against 2002 winner Lleyton Hewitt.
Defending women's champion Venus Williams is to play Alisa Kleybanova, and Serena Williams faces unseeded Bethanie Mattek, the only other remaining American. Those matches are back to back on Court 2 -- the "Graveyard of Champions" -- but the sisters will nonetheless be heavily favored, as usual at Wimbledon, where they've won six of the past eight titles.
Venus and Serena have settled into a groove on grass after enduring third-round upsets at the French Open -- only the second time both lost on the same day at a major event. Serena cleared Wimbledon's third-round hurdle Friday, and Venus was in a hurry to follow.
Her opponent was a Spanish left-hander with a lifetime record of 4-7 in Grand Slam matches. Predictably, Martinez Sanchez had no chance in baseline rallies, and the first set was a tennis clinic of sorts, with Williams whacking winners all over the court.
Her serve was especially impressive -- she finished with 11 aces and won 33 of 38 points on her first serve. Even Martinez Sanchez's supporters could appreciate the overpowering performance. "Vamos, Venus," someone shouted.
But in the second set Martinez Sanchez changed strategy and began to play serve and volley. It was a curious tactic to counter Williams' booming groundstrokes, like diving into the barrel of a howitzer, but for a while it worked.
Martinez Sanchez won three games in a row for a 5-4 lead. Then Williams began to treat her like slow traffic on the British motorway, passing her on the left, then on the right, then on the left again.
"I was pretty happy, because she started putting some pressure on, and I had some good answers," Williams said.
Williams won 12 of the final 14 points, the last with the record serve. At 127 mph, it topped the previous Wimbledon high of 126 achieved by both Venus and Serena. Venus holds the women's tour record with a 129 mph serve at last year's U.S. Open.
"The power that I have ... it's a real blessing," she said. "I'm actually never really trying to serve that hard, if that makes any sense. It just comes big. It's just how I serve. It's just me."
Williams celebrated the victory with her customary pirouette and wave, and as she left the stadium, she spotted a friend in the stands. She put her thumb to her ear and her little finger to her lips and mouthed the words "Call me."
Time to start making dinner plans for the second week.