Diego Costa said he always knew he would score again for Spain after netting twice in an 8-0 rout of Liechtenstein in its World Cup qualifying opener on Monday.

The Chelsea striker answered critics following a run of one goal in his 11 previous appearances for Spain by scoring the opener in the 10th minute, heading in former Atletico Madrid teammate Koke's free kick.

"I had struggled because a striker always needs to score goals but now I'm participating more in the play and I knew the goals were going to come," Costa said.