Wozniacki was the last player defaulted at US Open
First of all, Serena did not default yesterday. She was assessed a one-point penalty that happened to be enough to end the match. But since people asked who was the last person defaulted at USO (or a slam), the curious answer is Caroline Wozniacki.
This was 2006 when Caro played USO juniors as No.2 seed, right after her Wimbledon victory. She played Alexandra Panova the 1st round, leading by a set, then was defaulted after allegedly calling a linesman "f*cking a**hole!" Caro denied the charge, saying she "was talking to myself" but was sent packing anyway. Report said she stood outside players' lounge and cried for an hour.
Some have considered the treatment harsh, that the authorities just wanted to "set example" for juniors. It might have been a blessing in disguise.