Iran Press/ Europe: Diaz's superb 48th-minute solo effort secured a last-16 win to put the Spanish side in the driving seat ahead of the second leg at the Bernabeu, and the midfielder paid tribute to Bellingham by replicating his celebration.
The England international has 20 goals and eight assists in 29 games this season but is set to be sidelined for up to three weeks with a sprained ankle, and Diaz limped off before full-time at the Red Bull Arena in a fresh blow for Carlo Ancelotti.
The 14-time European champions misfired for long periods in Bellingham's absence and had Leipzig striker Benjamin Sesko made the most of the chances which came his way - and had Madrid goalkeeper Andriy Lunin not been in inspired form - the Spaniards might have had significantly more work to do on their own pitch on March 6.
Sesko headed into the net after Xaver Schlager had helped the ball back into the box from Lunin's punch as he dealt with David Raum's second-minute corner - but the goal was disallowed for offside against Benjamin Henrichs.
Sesko might have had a hat-trick inside the opening 10 minutes, failing to make the most of Xavi Simons' fine pass and then firing straight at Lunin, although Aurelien Tchouameni saw a ninth-minute header cleared off the line for Real, with goalkeeper Peter Gulacsi safely claiming Eduardo Camavinga's follow-up.
Henrichs then tested Lunin from distance, while Toni Kroos kept Gulacsi on his toes after Vinicius Jr had made his first real contribution down the left.
Camavinga produced a vital touch to deflect Sesko's 20th-minute attempt into the side-netting as Real continued to look vulnerable at the back, with Tchouameni having to make a vital challenge to deny Sesko before Vinicius stabbed wide after exchanging passes with Diaz in stoppage time.
But Bellingham's replacement broke the deadlock within three minutes of the restart - and he did so in spectacular fashion.
Picking up the ball wide on the right, Diaz span away from Raum and cut inside Simons and then Schlager before curling a left-foot shot across Gulacsi and inside the far post.
Leipzig would have been level almost immediately had Lunin not produced a double save from Dani Olmo and Sesko, and the 'keeper had to race from his line to prevent Sesko from latching onto Olmo's excellent through-ball as the Germans fought for a way back into the game.
At the other end, Schlager did just enough to put off Rodrygo as he ran onto Vinicius' 64th-minute pass after Real had broken at pace, and the Brazilian saw a shot come back off a post after he and Diaz had ripped the home defence to shreds with 19 minutes remaining.
Lunin produced a string of saves to deny Simons, Sesko and Amadou Haidara as Leipzig pushed for an equaliser, but the late assault proved to no avail.
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