Joseba Etxeberria condemned his former club Real Sociedad to their first defeat of the season as he inspired Athletic Bilbao to a 3-0 win over the Spanish Primera Liga division leaders at a rain-soaked San Mames.
The winger, who was snapped up by Athletic from their Basque rivals in 1995, scored two and made a third to provide a morale-boosting win for his side in a pulsating match.
Etxeberria scored his first when he drilled home from the edge of the area after a well-worked move from a free kick on 18 minutes.
He added a second when he cracked home on the turn from the edge of the box in the second half and then provided a superb pass for fellow midfielder Santi Ezquerro to grab the third deep into injury time.
Sociedad's disappointment at losing their unbeaten record was compounded when influential Turkish midfielder Nihat Kahveci was dismissed for a wild challenge on Bittor Alkiza four minutes from time.
Second-placed Real Madrid relied on spectacular second half strikes from Roberto Carlos and Luis Figo to come from behind to earn a 2-2 draw against relegation-threatened Espanyol.
The results mean that Sociedad's lead over Real is now down to four points, while defending champions Valencia are now breathing down Real's neck following their narrow 1-0 home win over a defensive-minded Real Mallorca.
Deportivo Coruna moved up to fourth after taking an important 2-0 away win over Real Betis, goals coming midway through the second half courtesy of strike pairing Diego Tristan and Roy Makaay.
Barcelona, meanwhile, continued their miserable run of form after crashing to a comprehensive 3-0 defeat at Atletico Madrid on Saturday.
The Catalan side, who have now lost three matches in a row, dropped to 15th place in the table.