It took Ronaldo just two minutes to extend his scoring streak to eight games as he headed home Gareth Bale’s cross and Karim Benzema made the game safe when he doubled Madrid’s lead just before half-time.
Bale teed up Ronaldo once more to make it 3-0 and the Portuguese then turned provider for Benzema to tap home his second of the game.
Ronaldo rounded off the scoring two minutes from time when he unintentionally deflected Pepe’s effort home to take his tally for the season to 17 goals in just 11 matches in all competitions.
Victory takes Real back to within four points of leaders Barcelona behind Valencia and Sevilla, but ahead of champions Atletico Madrid who drop down to fifth.
A fourth defeat in five league games for Athletic, meanwhile, means Ernesto Valverde’s men end the weekend in the relegation zone.
“We are improving in some aspects and we are growing,” said Ronaldo, who equalled the record of scoring 22 hat-tricks in La Liga also held by Telmo Zarra and Real Madrid legend Alfredo di Stefano.
“The team played a great game and scored five without conceding, so we are very happy.”
And Madrid boss Carlo Ancelotti lauded the contribution of his front three.
“All of the front three were fanastic. Cristiano scored three, Karim two and Gareth gave two assists and worked very hard for the team.
“Having the three of them working together is fundamental for the team.”
Bale provided the opener on his weaker right foot as he managed to pick out a perfect cross for the unmarked Ronaldo to head home at the back post.
Athletic ‘keeper Gorka Iraizoz then made a smart save low to his right to deny Ronaldo a second and Benzema just couldn’t stretch to turn home another Bale cross as the hosts piled on the pressure.
However, the Basques settled midway through the half and Iker Muniain’s spectacular dipping volley from the edge of the area forced Iker Casillas into action with a fingertip save.
Crucially Real managed to get the second goal before half-time, though, as Benzema rose highest to head Luka Modric’s corner in via the crossbar.
Bale wasted a great opportunity to make it 3-0 five minutes into the second-half as he blazed over with just Iraizoz to beat.
However, the Welshman made amends five minutes later when he raced onto Benzema’s pass and squared for Ronaldo to tap home his second of the night.
Bale came close again when he shot just wide after being set up by a lovely backheel from James Rodriguez and was then flagged offside when he did finally have the ball in the net.
Madrid were continuing to open up the Athletic defence at will and made it 4-0 21 minutes from time when Ronaldo unselfishly squared for Benzema to roll into an empty net rather than going for a hat-trick.
Ronaldo did then go in search of his third hat-trick in five games, forcing Iraizoz into a flying save with a powerful header.
However, the World Player of the Year wasn’t to be denied and registered his 26th hat-trick for the club, albeit with some fortune when he deflected Pepe’s effort past the helpless Iraizoz.
Earlier, Sevilla moved into third with a convincing 4-1 home win over bottom side Deportivo La Coruna.
Cameroonian midfielder Stephane Mbia continued his fine scoring form as he opened the scoring midway through the first-half, but Deportivo levelled soon after thanks to Haris Medunjanin’s free-kick.
However, Sevilla responded as Colombian international Carlos Bacca restored their lead before half-time and Mbia and Vitolo secured the three points with further goals after the break.