[VQdeochratis]

(a) Greg Rudeski

(b) Greg Rudeski, John McEnroe, Jimmy Connors, Guillermo Vilas, and that is all I can come up with for now.

Correct on (a).
Correct on (b) for three; I wasn't including Rusedski among the 6.

Add to (b) Manuel Orantes

Orantes only appearance in the US semis was in 1975, when he won... more than 30 years ago.

b. add the great Alexander Volkov. Remember he saved those mp's vs Muster late night on the grandstand

Correct on a fourth.

Need two more!!
(hint: both known for a big serve)