Momentum carries Serena past another Open test

— -- NEW YORK -- There are two ways Serena Williams' coach, Patrick Mouratoglou, knows she is on the right track, and her serve surprisingly is not one of them.

"She's good when she's calm or when she's angry, so it's either/or," he said. "Anything else is not good."

Of course, the serve helps. But in all ways, he said, the metaphorical switch was flipped midway through Williams' third-round win on Friday, with the six-time US Open winner's momentum carrying into her much-anticipated fourth-round match Sunday against Madison Keys and resulting in a decisive 6-3, 6-3 victory.

Williams' anger in dropping the first set Friday against Bethanie Mattek-Sands segued into third-set killer instinct then fourth-round calm, producing her best tennis of the tournament against Keys.

It comes in handy as she moves on to face a quarterfinal opponent she calls "the best player" in the draw. It will be Serena versus Venus on Tuesday, the 27th installment of one of the most emotionally fraught and unique rivalries in all of sports.

"At least there will be a Williams in the semis, so that's good," Serena said.

Better for those interested in witnessing history would be a Serena win, which would keep alive her chances for a calendar-year Slam and tie Steffi Graf -- the last player to accomplish the feat 27 years ago - for the second-most career Slam singles titles with 22.

But before meeting Venus, Serena had to take care of some necessary business against a formidable opponent in Keys. The 20-year-old American was seeded 19th here, but is among the most dangerous young up-and-comers in women's tennis with a power game evident in serve and groundstrokes not unlike Serena's.

As expected, both blasted away, Williams with a hardest serve of 121 mph and Keys nailing one at 124.

"I think I served pretty well," Keys said. "I think she returned better."

And that was really the story of the match, with Williams breaking Keys on three of eight attempts while not surrendering a single break point and committing just six unforced errors, only one in the first set. Williams also had no double faults after committing an uncharacteristic 17 combined in three previous matches.

For Williams, who benefited from Vitalia Diatchenko's first-round retirement, was admittedly tight in pulling out a first-set tiebreaker against qualifier Kiki Bertens in the second round and went on to drop the first set against Mattek-Sands in the third round. The task Sunday was relatively simple.

"If you're playing a great player, someone that knows how to win, you have to play better or you can go home," Serena said. "You can choose one."

Mouratoglou wanted Williams to put pressure on Keys' second serve and impose her game on the youngster.

"I want her to be very aggressive," he said. "She was not in the [second round] and I think she completely switched [midway through her third-round match] and came back. Serena has to hit winners. ... If she does, then she's very dangerous."

In other words, a loose Serena is a lethal Serena. Whether she will be able to keep it up against her sister, whom she has defeated in six of their past seven meetings and 15 of 26 matches overall, is why many will be watching their match Tuesday with one hand over their eyes.

"Yeah, I haven't really felt a lot of pressure," Serena said. "Only in that second round, for whatever reason, I got tight. The whole tournament I've been really kind of rather relaxed. I don't really feel like if I win this tournament it's going to make or break my career."

The room full of reporters laughed. So did Serena. She appears to be on the right track with three more victories to go. But observers will have to guess what's going on insider her head Tuesday.

"I guess I just try to be more internally excited," she said of her respect for her sister when the two play. "I still have a few 'C'mons,' maybe not as many, but I'm definitely obviously just as intense."