* Wales winger strikes in 38th minute
* Real held to 2-2 draw at Villarreal
* Barca leave it late against Sevilla (Adds details, quotes)
By Iain Rogers
MADRID, Sept 14 (Reuters) - Gareth Bale had a bitter-sweet start to his Real Madrid career when the world's most expensive player scored on debut but Real dropped their first points of the La Liga campaign in a 2-2 draw at promoted Villarreal on Saturday.
The Wales winger, who joined from Tottenham Hotspur for a record fee of 100 million euros ($133 million) earlier this month, struck in the 38th minute at the Madrigal to make it 1-1 after Cani had put the home side ahead in the 21st.
Playing in a three-pronged attack with Cristiano Ronaldo and Karim Benzema, Bale sped into the area and clipped a Dani Carvajal cross into the net with his right foot before being mobbed by his new team mates.
The 24-year-old, whose pre-season training was disrupted by the protracted negotiations over his move, was replaced by Angel Di Maria on the hour.
Ronaldo, the 94-million euro man who Bale succeeded as the most valuable player in soccer, netted a bizarre goal to put Real ahead in the 64th minute when his own shot cannoned back off a defender onto his leg and ricocheted into the net.
It was hard on an impressive Villarreal side, who were denied by a string of brilliant saves from Diego Lopez, but they were level in the 70th minute when Giovani Dos Santos, another former Tottenham player, lashed in a shot that crept into the net off the Real keeper.
The draw spoiled Real's perfect start to the season and they have 10 points from four matches, the same as Villarreal and two behind champions Barcelona and Atletico Madrid.
"It is very good news that he (Bale) scored on his debut," former Real forward Emilio Butragueno, now a club director, said in an interview with Spanish television broadcaster Canal Plus.
"But he has only been training with his team mates for three days and we have to wait for him to adapt," Butragueno added.
"He is a player with enormous potential and obviously we have a lot of expectations."
Barca had Alexis Sanchez to thank for maintaining their winning start after he came off the bench to score in the fourth minute of added time and snatch a 3-2 victory at home to Sevilla earlier on Saturday.
Barca have yet to settle under new coach Gerardo Martino and it was another unconvincing performance at the Nou Camp as they let slip a two-goal lead and were seconds away from dropping their first points of the campaign.
A rare Daniel Alves header against his former club put Barca ahead in the 36th minute before Lionel Messi looked to have made the game safe when he clipped a Neymar centre high into the net with 15 minutes left.
It was the World Player of the Year's sixth goal in three La Liga appearances this season.
Ivan Rakitic pulled a goal back when he smashed the ball past Victor Valdes in the 80th minute and Coke stole in to volley the equaliser 10 minutes later.
Messi again proved decisive in a dramatic finale, however, as he dashed to the byline before his cross fell to Alexis and the Chilean poked the ball into the net.
Although Barca were not at their best, Brazil forward Neymar, who joined from Santos for 57 million euros in the close season, had an excellent game and earned warm praise from Martino.
"It was really an impeccable performance from Neymar in every respect," Martino told a news conference.
"We were not sure how he would link up with Messi but we are already seeing that he is doing well," added the Argentine.
Atletico had far too much quality for Almeria on a festive afternoon for their fans packing a sun-bathed Calderon.
David Villa, who joined from Barca in the close season, struck with a superb left-foot volley after a quarter of an hour and Diego Costa scored from the penalty spot, his fourth goal of the campaign, in the 37th minute to make it 2-0.
Rodri pulled one back for the visitors three minutes later before Tiago scored from a well-worked free kick in the 64th and Koke killed the game off in the 67th when he cleverly flicked the ball into the net from close range.
Atletico took their foot off the gas in the final minutes and Almeria winger Alex Vidal swept into the area and beat Thibaut Courtois with a clinical shot in the 90th minute.
Atletico have won their opening four La Liga games for the first time since they last claimed the title in the 1995-96 season.
Real Sociedad, who like Barca, Real and Atletico kick off their Champions League campaign this week, drew 0-0 at Levante.
($1 = 0.7542 euros) (Editing by Justin Palmer)