A slip betwixt the cup and the lip.

　　A flash in the pan.

　　eg: Tom is disqualified at the final round, a slip betwixt the cup and the lip.

　　中英俚语俗语来源：汉书：“垂成之功，败于一日。”

　　同义词：功亏一篑 Look back from the plough.

　　反义词：一蹦而就 At one stroke.