Reeling from two cup exits in just eight days, Athletic sought redemption on home turf, with Nico Williams coming close to breaking the deadlock inside 20 minutes.
The winger’s looping effort seemed destined for the top corner, but Vicente Guaita produced a brilliant one-handed save to deny the Spanish starlet.
Celta, who attempted a season-high 23 shots in their defeat to Rayo Vallecano last time out, struggled to replicate such intensity in the absence of star forward Iago Aspas.
Instead, Guaita remained the hero of the first half, parrying Benat Prados’ sublime outside-of-the-boot strike over the bar to keep the visitors at bay in a half defined by his brilliance.
Claudio Giraldez introduced two fresh faces following the break, but it was Ernesto Valverde’s men who seized the initiative on the hour mark through Alex Berenguer.
The 29-year-old latched onto Inaki Williams’ precise pass from the right flank and coolly tapped his effort into the back of the net – only the second time in their last seven away league outings that they’ve opened the scoring.
Moments later, Dani Vivian extended Bilbao’s advantage with a stunning scissor-kick from point-blank range after Unai Gomez‘s headed pass found the centre-back lurking in front of goal.
Los Celestes soon halved the visitors' lead, though, with Hugo Alvarez pouncing on Adama Boiro’s costly defensive error inside the box, keeping the hosts within striking distance.
Nevertheless, Bilbao held firm to claim a fifth win in six trips across all competitions, with their last away league defeat coming in early October.
Only Atletico Madrid have now earned more LaLiga points than the Lions since the start of matchday 14, while Celta succumbed to a first defeat at home in three meetings. Following their 10th defeat this campaign, the Galicians linger in 13th position, only five points above the bottom three.