Espanyol midfielder Sanchez intercepted Bilbao goalkeeper Gorka Iraizoz's clearance and, having spotted a gap, risked using his less-favored left foot to fire a beautifully precise long-range shot that bounced in from high up the near post in the 24th minute.
''I don't think I've ever scored a goal like that,'' Sanchez said. ''We were lucky enough to be able to score first and finish the match with a win. We are a united team and that's the image that should be taken away from this match.''
Bilbao intercepted Espanyol's attack, quickly passed the ball to Benat Etxebarria who found Mikel Rico racing up the right flank, crossing precisely for Oscar de Marcos to score from the middle of the box in the 43rd.
Sanchez added a second goal in the 49th after a complex sequence of one-touch passes placed the ball precisely onto his right foot.
As Espanyol surged forward, Iraizoz saved three shots on goal in rapid succession only to have the fourth bounce off him into goal after Sergio Garcia's close-range shot in the 66th.
Bilbao has not won at the Cornella stadium in 15 years.
We found it hard to get into the match, Espanyol tends to pressure you well, especially at the beginning of matches,'' said Bilbao forward Iker Muniain. ''We were on the brink of equalizing at the end, but we've got another match Thursday so it's time to think about that.''