Conversation so far:
what occurred in 1972 to Ken Rosewall?
Rosewall won seven tournaments in 1972, including the depleted Australian Open and became the oldest Grand Slam male singles champion (37 years and 2 months old) in the open era
what was a tournement Ken Rosewall played in?
Rosewall won seven tournaments in 1972, including the depleted Australian Open
who was an opponent of Ken Rosewall?
Ken Rosewall defeated Australia Malcolm Anderson 7–6, 6–3, 7–5
Ken Rosewall did not defeat any opponents?
Ken Rosewall defeated Australia Malcolm Anderson 7–6, 6–3, 7–5
What was Ken Rosewall's performance in the US open?
He lost in the second round of the 1972 U.S. Open against Mark Cox.
what was the score when Ken Rosewall lost in the second round of the 1972 U.S. Open against Mark Cox?
6-1, 3-6,6-7, 6-7
what is a notable title Ken Rosewall won?
At the 1971 Australian Open he became the first male player during the open era to win a Grand Slam tournament without dropping a set.
did Ken Rosewall have any injuries?
During his long playing career he remained virtually injury-free

Question: what was his highest ranking?
Self-contained rewrite: what was Ken Rosewall's highest ranking?