Tagger’s serve and first-strike tennis can make a match lively without making it brief. She has had trouble turning good positions into clean finishes: against Ann Li in Osaka, she missed a late break chance and then lost the deciding tie-break heavily.

Williams has not played singles recently, but she found more rhythm as her US Open match with Sofia Kenin went on, reaching a second-set tie-break and creating chances to extend it. Her doubles appearance in Guangzhou gives her fresh match play, while Tagger is backing up a demanding Osaka week that included an extended quarterfinal and doubles the same day.

Over 17.5 at 1.74 has room to breathe: even 6-3, 6-3 gets there, and a set for Williams would make the total a comfortable ride. Tagger’s serve can hold up, but her recent tennis has not consistently produced the return-game dominance needed for a quick demolition.

The caution is plain enough: if Williams’s movement falters, Tagger could run through a set 6-1 or 6-2, as Williams has in some summer losses. That keeps this a modest-conviction play; I have not assessed another market or line.