Osasuna 0-0 Atlético Madrid
Portillo came up through the ranks at home-town club Real Madrid and he was given the perfect opportunity to help sink his old side's bitter rivals Atletico when Osasuna were awarded an 18th-minute spot-kick.
However, despite striking his shot well, Portillo's effort was not good enough to beat visiting goalkeeper Gregory Coupet, who flung himself to his left to palm the penalty away.
That would prove to be the best chance either side would have to take the points in a low-key encounter where the draw will have left both clubs a little disappointed.
Osasuna, as the last remaining team in La Liga without a victory, have obvious reasons for feeling they could have been celebrating a three-point haul, while Atletico will be upset they missed the chance to put more pressure on the teams at the top.
The Rojiblancos travelled north on the back of a five-match unbeaten run in all competitions, the latest of which was their 1-1 draw at Liverpool in the Champions League on Tuesday, but they looked to be in trouble after conceding that early penalty at the Reyno de Navarra.
The kick was given following Mariano Pernia's challenge on Santi Ezquerro in the box as both players battled for a long ball forward.
It was a debatable decision, and Atletico will feel justice was done as Coupet produced a superb save to keep out Portillo's resulting penalty.
Atletico were unable to build on that let-off though as the points were shared.
Osasuna enjoyed the better of the chances in the opening period but Atletico improved after the break following the arrival of striker Diego Forlan, who had started the game on the bench.
The Uruguay international then had a decent chance to put his side ahead in the 73rd minute, but he could not finish the opportunity as Osasuna survived.
There would be no late heroics from either side as the game finished in stalemate, meaning Javier Aguirre's expensively-assembled side are now already 11 points behind leaders Barcelona with only 10 games gone.
For Aguirre's former club Osasuna, the goalless scoreline cannot be considered too much of a surprise considering only 12 goals had been scored in total in their previous nine league games - with only three being claimed by the Pamplona-based side.
The silver lining for new coach Jose Antonio Camacho is that Sunday's draw ends a run of three straight league defeats since the former Spain coach replaced Jose Angel Ziganda in the hotseat last month.
Next weekend Osasuna travel to second-bottom Athletic Bilbao in what could prove to be a key battle between two sides hoping to escape from the relegation zone.