NEW YORK, NY, USA -- Six-time US Open champion Serena Williams of the United States eased past Karolina Muchova of the Czech Republic, 6-3, 6-2 on Friday to reach the round of 16 at the US Open for the 18th time in her storied career.

"Had to go out there on business," Williams said, in her post-match press conference. "I think I tried to do that with all three matches thus far. It was just different because I know that [Muchova] could play today. I knew what she could do."

No.8 seed Williams fell in the third round of her first-ever US Open in 1998, but since that loss, she has been undefeated in third-round matches at her home Grand Slam event, improving to 18-1 overall following her 73-minute victory over World No.44 Muchova.

GALLERY: 20 years on at Flushing Meadows: The story of Serena Williams' first Slam

23-time Grand Slam champion Williams played a precise match with 20 winners to 15 unforced errors -- seven of those unforced errors being double faults. At the end of the day, Williams converted four of her seven break points to zip to victory.

"Like I said on the court, I don't know how I would grade my performance," said Williams. "Just gotta keep playing and believing."

Muchova reached the third round of the US Open last year as a qualifier ranked just outside the Top 200, and has zoomed up the rankings since then due to excellent results, including reaching the quarterfinals of her Wimbledon main-draw debut. The Czech, though, could only win 36 percent of points on her second serve against Williams in their first meeting.

Williams will face No.22 seed Petra Martic of Croatia in the fourth round. Martic, who is having a breakthrough season after winning her first WTA singles title in Istanbul and reaching her first Grand Slam quarterfinal at Roland Garros, dismissed No.12 seed and 2018 US Open semifinalist Anastasija Sevastova of Latvia in straight sets earlier on Friday.

After holds by both players in the first two games, Williams began to impose herself on the Czech’s delivery with thunderous returning. The American held three break points in Muchova’s next two service games, but the Czech came up with fine serves and devilish volleys to eke her way out of those jams and stay with Williams through 3-3.

Williams, however, kept up her aggressive mindset, and put away a midcourt forehand in the 3-3 game to earn two more break points. The American finally converted her fourth chance overall after Muchova sent a forehand long, giving Williams a break lead at 4-3.

The American then jumped to a 40-15 lead in the next game, but after a Muchova return clipped the netcord for a winner to bring the game to deuce, Williams double faulted to give Muchova her chance to put the set back on serve. But Muchova netted a return there, and Williams eventually held with a forehand crosscourt winner.

Williams cruised from there in the first set, blasting winners from both wings to move to triple set point on the Muchova serve. A fierce forehand return winner closed out the opening fame in favor of the six-time US Open champion, which was her 13th winner of the set, opposed to just eight unforced errors.

Muchova double faulted away her first service game in the second set as Williams slid to a commanding 3-0 lead. But the Czech broke Williams for the first time in the match to get back on serve at 3-2, after the American misfired on critical volleys.

However, that was a minor blip in Williams’s race to the fourth round, as she regained the break lead for 4-2, and consolidated with her powerful game to put herself one game away from victory. Williams gave herself two chances to close out the match on Muchova’s serve with a forehand crosscourt winner, and took the win after the Czech sent a forehand long on the first match point.