Goncalo Ramos gave Benfica the lead after 15 minutes as he headed the ball in from Joao Mario’s corner.
But the advantage didn’t last long as Miguel Almiron started and finished a fine attacking move to turn the ball in from Kieran Trippier’s cross.
Benfica restored their advantage as Alex Grimaldo curled a 25-yard free-kick into the top right corner of the goal.
But Trippier and Almiron combined again as the Paraguayan levelled the score at 2-2 going in at half-time.
Newcastle finished the match with 10 men after Joelinton was shown a second yellow card with nine minutes remaining.
Benfica made their man advantage count in the final minute of normal time as Henrique Araújo stroked home to make it 3-2.
9. Miguel Almiron - 9
Came close to giving Newcastle the lead inside the opening four minutes. Looked full of confidence as he brought the ball forward and grabbed an equaliser from close range. Equalised again on the stroke of half-time with a tidy finish. Has been like a new signing this pre-season with six goals to his name, an average of one every 44 minutes. Photo: Ian MacNicol
10. Allan Saint-Maximin - 7
Got on the ball and posed a threat in possession. Dragged an edge-of-the-box effort wide of the left post after cutting inside. | Getty Images
11. Callum Wilson - 6
Showed good strength and power to lead the line on his own. Had a decent chance to give Newcastle the lead but the offside flag went up. Photo: Stu Forster
12. Karl Darlow - 6
On for Pope 46: Was alert to come off his line and stop Benfica taking the lead in the second half. Photo: Ian MacNicol