The decisive goal came in the 36th minute when Inter’s Serbian midfielder Dejan Stankovic played the ball over the top to Crespo who unleashed a fierce first-time shot past Sporting keeper Ricardo.
In the same group Radoslav Kovac’s second-half strike salvaged a point for Spartak Moscow as they drew 2-2 with Bayern Munich.
The draw left Spartak with a slim chance of finishing third in Group B and qualifying for the UEFA Cup.
The German champions are already through to the last 16.
The Russians drew first blood when Ukraine international Maxim Kalinichenko wrong-footed Oliver Kahn with a curling free kick into the bottom far corner from 20 metres in the 16th minute.
It was the first goal conceded by the German champions in the Champions League this season.
But Claudio Pizarro quickly restored order, striking twice in the space of 17 minutes to put Bayern 2-1 ahead.
Pizarro, who also scored in the 4-0 thrashing of Spartak in their first meeting in Munich two months ago, equalised in the 22nd minute after a quickly taken corner, flicking a header past Spartak’s third-choice keeper Alexei Zuyev.
The Peru striker then beat Zuyev with a 30-metre blast into the top corner in the 39th minute.
The Germans were content to play it safe after the break but Czech Republic international Kovac secured a point for the home side, hitting the target from close range after a corner in the 72nd minute.
In Liverpool’s group Bordeaux qualified in style for the UEFA Cup last-32 with a 3-1 thrashing of Galatasaray in the south of France.
With Rafa’s Benitez’s men earning top spot ahead of PSV Eindhoven at Anfield, this match-up was a dead rubber. The French side, however, made sure they would finish third in Group C with goals from Alejandro Alonso, Lilian Laslandes and Julien Faubert.
Galatasaray scored a consolation goal 17 minutes from time through former Arsenal midfielder Junichi Inamoto after having midfielder Turan Arda sent off on the hour. Bordeaux, who have four points from five games, lead the Turkish side by three points.
They held Galatasaray to a goalless draw in their previous meeting.
In Group D, goals either side of half time from Miguel Angel Angulo and Fernando Morientes gave injury-ravaged Valencia a 2-0 win at home to Olympiakos Piraeus that ensured them first place.
Olympiakos made a bright start at the Mestalla, but fell behind when Angulo curled a shot into the far corner on the stroke of half time.
Valencia hit them again a minute after the break; Morientes with a trademark header at the far post.
With AS Roma slipping to a 1-0 defeat at Shakhtar Donetsk, Valencia top the group with 13 points, six clear of the Serie A side, and eight ahead of the Ukrainians. Olympiakos are bottom with two points.
Ciprian Marica was the hero as he headed home in the 61st minute to give Shakhtar Donetsk a famous victory over the Italians.