International Champions Cup: Atletico Madrid 0-1 Inter Milan
Forward Martinez scored the only goal of the game in the 31st minute against the club he nearly joined last year, acrobatically putting away Kwadwo Asamoah's cross-field ball to stun the home side at Wanda Metropolitano.
The Argentine forward, who was signed by Inter from Racing Club in July, also demonstrated his blossoming partnership with Mauro Icardi early in the first half, sending his compatriot through on goal in the 11th minute.
Jan Oblak rushed from his line to smother Icardi’s chipped attempt on that occasion, but the Atletico goalkeeper could do little to prevent the game's eye-catching winner just after the half-hour mark.
Allowed to carry the ball down the left flank on the counter, Asamoah spotted Martinez free at the back post, floating over a cross that his team-mate converted in spectacular fashion.
Atletico thought it had equalised before the break when Angel Correa converted Koke’s through pass, only for the strike to be ruled out for offside by the video assistant referee. The use of technology was a relief for Inter defender Miranda, who had carelessly surrendered possession on the edge of his own penalty area to set up the opportunity for his former employer.
The home side upped the tempo after the break, Diego Costa — booked in the first half for dissent — heading over before Juanfran saw a firm drive blocked by the outstretched Dalbert.
Samir Handanovic kept out Vitolo's header with a reactionary save as Inter held on, although the result was not enough to see it overhaul Tottenham Hotspur to finish the pre-season tournament in top spot.
Atletico faces the small matter of a derby fixture against neighbour Real Madrid in midweek, as the two Spanish clubs face each other in the UEFA Super Cup in Tallinn, Estonia, on Thursday (AEST).
Inter, meanwhile, has to wait a little longer for its next outing. It starts the Serie A season with a trip to Sassuolo next Monday (AEST).