Jonas gives Valencia upper hand over Sevilla
The Brazilian forward's first-half strike leaves the tie finely balanced ahead of next week's second leg in Seville and the winners will play Levante or second-division Alcorcon in the quarter-finals.
Alcorcon, who eliminated Real Zaragoza in the last round, snatched a 2-1 win at home to Valencia-based Levante on Tuesday.
Holders Real Madrid and last year's runners-up Barcelona are on course to meet in the last eight after the great rivals both won their first legs this week.
Real came from two goals down to beat Malaga 3-2 on Tuesday and Barca thrashed Osasuna 4-0 on Wednesday.
On the other side of the draw, second-division Cordoba claimed a 2-1 comeback win over top-flight side Espanyol earlier on Thursday.
Third-tier Mirandes opened a 2-0 lead over visiting Racing Santander on Tuesday, while another Segunda B side, Albacete, drew 0-0 at home to Athletic Bilbao.
Real Sociedad, Cup winners in 1987, beat 2003 champions Real Mallorca 2-0 on Wednesday.