Xanthi won 2-1 away to AEK Athens in the Greek capital on Sunday on the opening weekend of the Greek Super League season.
The hosts were reduced to ten men when Francisco Geraldes was sent off for a second yellow card offence after just 33 minutes.
Xanthi opened their account through substitute William - who'd only been on the pitch for six minutes - midway through the second period and doubled their lead 11 minutes later through Jean Barrientos.
Nelson Oliveira netted a consolation goal for AEK just before the final whistle.
