Conversation so far:
What is Masters?
Masters Tournament.
When was this?
April 11.
Did he win the the tournament?
The win marked the third Masters victory for Mickelson and his fourth major championship overall.
What was his final score?
he was in close contention throughout for the lead and finished tied with Choi for 4th at -11.

Question: Who else was in the tournament?
Self-contained rewrite: Who else was in the Masters Tournament on April 11th other than Phil Mickelson?