© Getty Images
However, the Espanyol captain found the target just moments later, driving a powerful strike into the bottom corner.
Perez looked to set up Christian Stuani to double the visitors' lead later in the first half, but the home keeper made the save from point-blank range.
Artiz Aduriz almost scored an equaliser just before the half-hour mark, but his header clattered back off the crossbar.
The goal triggered a Bilbao resurgence, with Aduriz almost putting the home side ahead, only to be denied by a Colotto block.
Colotto was involved at the other end just a couple of minutes later as he restored Espanyol's lead, tapping in from a Simao corner.
The home side's hopes of finding a late equaliser were dashed when Aduriz picked up his second yellow card of the match in the final five minutes for a late challenge on Victor Sanchez, forcing Bilbao to finish the contest with only 10 men.
The result moves Espanyol up to seventh in the table.