The Welshman collected his 10th goal of the season and his 11th for the club in Europe with just five minutes gone to give them the point they needed to avoid the Champions League drop-outs in the last 32.
Sporting responded with a 39th-minute equaliser from Custodio, but a Magpies' side comprising the only fit 11 senior players at the club, and a bench they could not fill, fought manfully to hold on.
This was a performance of grit and character on a night when qualification had already been assured, but there was still a major prize at stake.
There was no Alan Shearer, Patrick Kluivert, Kieron Dyer, Nicky Butt, Laurent Robert and Lee Bowyer, but there was heart and resilience in front of a crowd of just 28,017.
Newcastle, having lost to Sporting in a pre-season tournament, knew they faced a stern test and so it proved as the visitors claimed more than their fair share of possession and passed the ball with style and adventure.
However, they were met, for once, by a solid black and white wall as the club's only four fit defenders, aided by a hard-working team display, managed to keep them at bay for all but a few fleeting moments.
Manager Graeme Souness admitted in the run-up to the game he did not know whether to expect an onslaught from the first whistle or a cagey game, but he was in little doubt after a lively opening from Jose Peseiro's men.
It was with pure delight, then, that he saw his side take the lead within five minutes of the kick-off.
Shola Ameobi rose well to meet Titus Bramble's deep free-kick and send the ball into the penalty area, where Bellamy pulled away from marker Roberto Beto to send a looping header over keeper Ricardo.
Sporting were not about to sit back and accept their fate, and with Fabio Rochemback and Paulo Tinga dominating in central midfield, they continued to make the running, although without working Shay Given.
But they looked vulnerable at the back, particularly to the pace of Bellamy, and he should have made it 2-0 after 24 minutes when he beat the offside trap to collect Steven Taylor's ball, but shot straight at Ricardo's legs.
At the other end, his team-mates had a few uneasy moments attempting to keep the visitors out, but as their frustration increased, Belgian referee Paul Allaerts began to make his mark.
He rightly booked Bramble for a rugged challenge on striker Liedson, but ignored the Brazilian's shameful play-acting, and he had little choice but to show Ameobi a yellow card after he threw the ball away in disgust.
However, Aaron Hughes felt aggrieved to suffer the same fate six minutes before the break for a challenge on Martinho Paito, and from the resulting free-kick, Custodio powered a header past Given to level.
An even contest continued in the same vein after the restart as both sides used the ball well but were continually thwarted by committed defence.
Ameobi forced Roberto Beto to concede a 50th-minute free-kick which Darren Ambrose drilled in to the near post to cause Ricardo a momentary problem.
Sporting were still moving the ball well and Newcastle looking dangerous on the counter, and with everything to play for, the tension was mounting.
The visitors were claiming a penalty after Liedson went down under Olivier Bernard's 65th-minute challenge, and the pressure mounted on the Magpies as the clock ran down.
Rochemback failed to test Given fully with a mishit free-kick 17 minutes from time after James Milner had felled him, but Souness soon shored up the defence when he sent on Andy O'Brien for Taylor five minutes later.
Souness' problems deepened seconds later when Bellamy limped off injured to be replaced by teenager Lewis Guy.
The Magpies found themselves pinned back as the final whistle approached, but they were not about to let their point slip at the death.
: Given, Taylor (Andrew O'Brien 78), Bramble, Elliott, Hughes, Milner, Ambrose, Jenas, Bernard, Bellamy (Guy 79), Ameobi.
: Ricardo, Beto (Tello 83), Anderson Polga, Enakahire, Paito, Rogerio, Rochemback, Custodio, Tinga, Pinilla (Douala 66), Liedson.
: Paul Allaerts (Belgium).