Real's city rivals Atletico, in their first match since Friday's sacking of coach Abel Resino, had earlier conceded a farcical last-minute equaliser to draw 1-1 with nine-man Real Mallorca, and third-placed Sevilla were held 0-0 at home by Espanyol thanks to a string of superb saves by Carlos Kameni.
Manuel Pellegrini's Real side were hoping for a confidence-boosting win at a rain-drenched Molinon after Wednesday's 3-2 Champions League loss to AC Milan.
But Gonzalo Higuain and Karim Benzema had joined Cristiano Ronaldo and Ruud van Nistelrooy on the injury list, leaving Raul as the only recognised forward, and they found it tough to break down a spirited Sporting side.
Real goalkeeper Iker Casillas had to be alert to deny in-form forward Miguel de las Cuevas just before halftime, before Esteban Granero prompted a fine save from Juan Pablo after good work from Kaka.
Real had the lion's share of possession in the second period and pressed for a winner, Xabi Alonso flashing a drive over the bar and Raul having an effort ruled out for a Kaka handball.
Tempers began to fray as the tension mounted, and Mahamadou Diarra appeared to lash out at Alberto Rivera, but with Pellegrini looking an increasingly forlorn and soggy figure on the sidelines Sporting held on for a deserved point.
NUMERICAL ADVANTAGE
Pellegrini said he was unhappy to have missed out on three points and praised Juan Pablo for keeping his players at bay.
"Sporting have a lot of intensity, a strong attacking line and technical ability," the Chilean told a news conference.
Atletico's miserable season took a turn for the worse a day after Resino was replaced by Quique Sanchez Flores and they are down in 14th place with only one win from eight matches.
Diego Forlan missed one penalty in the first half but recovered to net another, only for teenage goalkeeper David De Gea to allow Borja Valero's tame cross-shot to deflect in off his legs in the final minute of normal time.
Resino's assistant Santi Denia was in charge of the side and Atletico's players looked keen to impress the watching Sanchez Flores in the early stages at the Calderon.
Their efforts appeared to have been rewarded in the 27th minute when the referee ruled defender Josemi had handled the ball in the penalty area and showed him a second yellow card.
Forlan stepped up to take the spot kick but blasted wide of the right post.
The Uruguay striker was given a second chance five minutes into the second half when Ivan Ramis handled in the area and was also shown a second yellow.
Forlan sent Mallorca goalkeeper Dudu Aouate the wrong way, side-footing low into the bottom right, but Atletico were unable to press home their numerical advantage.
Valero picked up a deep cross at the far post in the 90th minute and when De Gea tried to clear his cross-shot from a tight angle he only managed to send the ball into his own net.
Espanyol's Cameroon keeper Carlos Kameni was on inspired form at the Sanchez Pizjuan, producing
