Steal sb's thunder: spoil sb's attempt to surprise or impress, by doing sth first 抢在某人前头,抢先做,抢某人功劳

He had planned to tell everyone about his discovery at the September meeting, but his assistant stole his thunder by talking about it beforehand.
他原本计划在9月份的会议上向大家宣布他的发现,可是他的助手却抢先说了这件事.

Upstage: to say or do something that makes people notice you more than the person that they should be interested in 抢...的镜头;把对...的注意吸引过来

She was furious at being upstaged by her younger sister. 她被妹妹抢去风头,感到气愤不已.