Conversation so far:
what occurred regarding ken rosewall in 1972?
From August 1972 players could enter almost all the tournaments they wanted and the real open era began.
what was a tournement he played in?
Rosewall won seven tournaments in 1972.
who was an opponent?
Mark Cox.
he did not defeat any opponents?
He lost in the second round of the 1972 U.S.
Open against Mark Cox.
What was his performance in the US open?
His best performances in 1973 were firstly his semifinal at the US Open.
what was the score?
CANNOTANSWER.
what is a notable title he won?
He also won at Houston WCT, Cleveland WCT, Charlotte WCT, Osaka and Tokyo.
did he have any injuries?
CANNOTANSWER.
what was his highest ranking?
He was still ranked in the top 10.
Tommasi ranked Rosewall 4, Tingay 6, ATP 6, Collins 5, and McCauley 7.
did he ever have a drop out?
CANNOTANSWER.

Question: what was his best year during this time?
Self-contained rewrite: What was Ken Rosewall's best year between 1972 and 1980?