Bruno Gama had Depor dreaming of a fifth successive victory with his 38th-minute strike but Llorente headed Athletic level just before the break to earn a point for the Basque outfit, who were forced to hold on with a man less for the final nine minutes following the dismissal of Ander Iturraspe.
Llorente has been Athletic's leading goalscorer for the last five seasons but he had netted just once in La Liga this term before today after being given limited playing time since announcing last summer his intention to quit the club.
The Spain international, who is joining Juventus at the end of the season, was named in Marcelo Bielsa's starting line-up today and he was in the thick of the early action with three attempts on goal in the opening 17 minutes.
However, none of those troubled home keeper Daniel Aranzubia - Llorente's former Athletic team-mate - and it was Depor who would end up taking the lead through Gama.
The former Porto player found the roof of the net from the edge of the box to get on the scoresheet for a third successive game.
Depor's lead lasted just six minutes, though, before Athletic got back on terms through that man Llorente, who again showed his aerial prowess to nod home Andoni Iraola's right-wing cross.
That proved to be the end of the scoring, although both sides came close in the second half - none more so than Llorente and his team-mate Markel Susaeta.
Both players saw efforts came back off the frame of the goal in succession in the 69th minute, with Llorente shooting against the post before Susaeta fired the rebound against the bar.
Relegation-battling Depor responded with Ivan Riki and Paulo Assuncao shooting over and Luis Pizzi bringing a save out of Iraizoz.
The home side received a big boost in the 81st minute when Athletic were reduced to 10 men, Iturraspe handed a second yellow card following a foul on Gama.
However, Depor could not make the most of their numerical advantage with their best effort seeing Assuncao's shot saved by Iraizoz.