Luis Suarez once more made it to the scoreboard as FC Barcelona stayed on course for a place in the final of Copa del Rey for a record fifth straight year.
Suarez scored a second-half winner off a cross by Messi as Barcelona defeated Valencia 1-0 in the first leg of the semifinals on Thursday.
The three-time defending champion had difficulty getting past the Valencia defense at Camp Nou Stadium until Messi came through with a great play midway through the second half.
Messi controlled the ball inside the area and calmly carried it toward the end line, attracting three Valencia defenders. As they converged, he sent the ball all the way across the area to Suarez, who was free to score with a firm diving header.
The second leg is next week at Mestalla Stadium.
Valencia is trying to win its eighth Copa title, and the first since 2008. Barcelona has a record 29 titles.
Five-time champion Sevilla drew at Leganes 1-1 in the first leg of the other semifinal on Wednesday. The return match is next week in Seville.