Williams won six of her Grand Slam singles titles - plus 30 WTA tournaments - before Austria's Tagger was born in February 2008.
Tagger's coach Francesca Schiavone - the Italian former world number four who won the 2010 French Open - is the same age as Williams, and lost all eight meetings with the American during her playing career.
"When I saw the draw I was super excited and a bit nervous - I respect her a lot," said Tagger, who is 53rd in the world.
"It is funny she used to play with my coach. I would love to play at this age - I want to congratulate her."
While the straight-set scoreline will embolden the critics, Williams did make Tagger - a rising talent who is predicted to have a bright future at the very top - work hard.
However, the teenager proved far too good. The 2025 French Open girls' champion was superb on serve - dropping just seven service points and not facing a break point - while handling Williams' pace and crushing groundstrokes off both wings.
Tagger broke her illustrious opponent's serve twice - for 1-0 and 5-2 leads - in two almost identical sets.
At times, Williams was able to use her powerful serve to get out of trouble - fighting off 12 of 16 break points - and the veteran's trademark competitive spirit never wavered.
But it was another example of how far behind the rest of the tour she now is.