Father time remains undefeated, or so the saying goes. However, a couple of months on from her 36th birthday, Williams continues to defy the aging process, taking the best part of three hours to defeat Kozlova, 6-2, 5-7, 6-4.
The tennis landscape is much changed since a teenage Williams - accompanied by beads and garish outfit - made her Grand Slam bow against Naoko Sawamatsu at the 1997 French Open. Remarkably, the American, now an iconic figure in the sport, remains a threat at its four flagship events.
Last year, quarterfinal appearances at both the Australian and US Opens - backed up by no little success elsewhere - propelled Williams back into the Top 10. And this campaign she has maintained the momentum, reaching the semifinals at the site of her greatest triumphs, the All England Club.
At Wimbledon, Williams matched Amy Frazier's Open Era record of 71 Grand Slam appearances, marking the occasion with rollercoaster victories over several of the game's brightest young talents. Against Kozlova - who was just three years old when Williams made her US Open debut - she was once against forced to draw on her wealth of experience.
? ESPN Stats & Info (@ESPNStatsInfo) 30 August 2016
The 2000 and 2001 champion has never lost an opening round match at Flushing Meadows, a statistic that looked in little danger when she pocketed the first set and moved 4-2 ahead in the second.
Kozlova, though, had other ideas, silencing the partisan crowd by rattling off five of the next six games to take the match the distance. A similar story looked to be unfolding in the decider, the Ukrainian falling 5-2 behind only to produce an unerring down-the-line backhand to break back in the ninth game. This time she was unable to complete the comeback, erring on the backhand to succumb the following game.
Despite a messy afternoon the No.6 seed, who finished with 63 unforced errors, was characteristically upbeat afterwards. "The errors told the story today," Williams said. "Once you're at this level everyone can play. Today I had to hit a lot of balls and I think that will help me going into the rest of the tournament."