From wiki:

Ace: Serve where the tennis ball lands inside the service box and is not touched by the receiver; thus, a shot that is both a serve and a winner is an ace. Aces are usually powerful and generally land on or near one of the corners at the back of the service box. Initially, the term was used to indicate the scoring of a point.

Winner: A shot that is not reached by the opponent and wins the point; sometimes also a serve that is reached but not returned into the court.

Ace没啥争议，就是接发球方没有碰到入区球。
Winner定义确实有点含糊，我见到的多是指“相持球”中如果对手没有碰到球。及“发球”中对方碰到球但打丢了的，至少解说基本上都是这么称呼的。

【 在 Litmanen 的大作中提到: 】
--
FROM 108.31.102.*