Fed is only told 5 mins before the match he must use an old wooden racket. Best of 3 so he doesn't have long to adjust.
Who wins?
Depends on what Fed we are talking about against a specific Serena. At their current ages, Fed takes it in 3.
Serena would command the first set, but Fed, knowing he needs to find out how to play this racquet, takes it easy, rallies longer, pushes.
2nd: Fed plays more aggressively, making more faults, but more crucial points when he needs them. Gets broken twice, breaks back twice. In the tiebreak, he hits his stride with an I/O backhand straight down the line for 7-6 (6).
3rd- Federer is used to the racquet, and gets to defend 3 BP, all of whiche he does successfully. He breaks Serena once, as she plays defensively to counter Fed. Given Fed's superior physicality, he beats her convincingly in this set.
2nd set could go either way, but if Fed uses the first set correctly, he takes the 2nd and 3rd.