* Struggling Real lose 1-0 in Granada
* Fifth defeat on the road this season
* Barca can extend lead over Real to 18 points on Sunday (Adds details, other games, quote)
MADRID, Feb 2 (Reuters) - Cristiano Ronaldo scored the first own goal of his career to send Real Madrid to a shock 1-0 defeat at lowly Granada in La Liga on Saturday, further damaging their already slim hopes of retaining the title.
Ronaldo has scored 21 league goals this season but headed into his own net at a corner in the 22nd minute and his side rarely threatened after that in the face of resolute opposition.
The result left the champions 15 points adrift of leaders Barcelona, who can extend their advantage over their great rivals to 18 with a win at Valencia on Sunday.
Real have 43 points from 22 games and remain four points behind second-placed Atletico Madrid, who host Real Betis on Sunday.
"We played a bad game, the responsibility is mine," Real coach Jose Mourinho told a post-match news conference.
"The result bothers me. The first half was horrible, and although we improved in the second half, it wasn't enough.
"Granada defended with heart and soul, and a lot of motivation, and it was a great night of football for them."
Wednesday's King's Cup semi-final first leg at home to Barca, when Real recovered to grab a 1-1 draw, seemed to have taken its toll as Mourinho's side struggled to get going.
Their hard-running hosts, inspired by a change of coach from Juan Antonio Anquela to Lucas Alcaraz on Wednesday, took advantage of a familiar failing for Real this season when they went ahead at a corner.
Ronaldo rose at the near post and skimmed the ball past Diego Lopez and into the roof of his own net.
The visitors slowly found their feet but failed to register a single shot on target before halftime.
Mourinho threw on forwards Karim Benzema and Jose Callejon in a double substitution to try and pep up his team, and Ronaldo became more involved in the game.
The Portugal forward tested goalkeeper Tono on a few occasions but it was Callejon and Benzema who had the best chance between them to level in the 84th.
Callejon dribbled into the area and was denied by Tono but when the ball broke to Benzema he scuffed his shot wide of the far post in front of an open goal.
Real have now lost five games on the road this season, four of them in Andalusia after setbacks at Sevilla, Real Betis, Malaga and Granada. The other one they lost at Getafe.
Levante missed the chance to move into the Champions League places when they lost 3-2 at improving Espanyol.
An own-goal from Vicente Iborra put the visitors behind just before the break.
Ruben Garcia headed Levante level after an error in the home defence, but Javier Aguirre's Espanyol struck twice in two minutes to seal the win.
Sergio Garcia crossed for Christian Stuani to head Espanyol's second, and then scored from the edge of the area before Obafemi Martins burst clear to pull one back for Levante at the end.
Troubled Deportivo La Coruna remain rooted to the foot of the standings after a 3-1 defeat at Getafe, despite taking the lead against 10 men at the Coliseum.
Home keeper Miguel Angel Moya was sent off after 10 minutes and Pizzi netted with a penalty but Diego Castro levelled with another spot kick at the other end in the 25th.
Depor had midfielder Abel Aguilar sent off in the 71st and Getafe took all the points when Alvaro Vazquez and Adrian Colunga grabbed well-taken goals near the end
Osasuna climbed out of the bottom three with a 1-0 home win over Celta Vigo in the day's other game. (Reporting by Mark Elkington, editing by Ken Ferris)