Martinez and Lo Celso send Argentina through in painful blow for Venezuela
Martinez gave Argentina a 10th minute lead with a clever back flick between his legs and substitute Lo Celso secured the victory 16 minutes from time, pouncing on a mistake by Venezuela's goalkeeper Wuilker Farinez at Rio de Janeiro's Maracana stadium.
It was another improved performance from Lionel Scaloni's team who have grown into this tournament since beginning with a 2-0 defeat to Colombia and a 1-1 draw with Paraguay.
They are bidding to end a 26-year wait for a major international trophy.
Argentina started like a team determined to claim the prize at stake: a semi-final against their great rivals Brazil.
Martinez played in Sergio Aguero in the inside right channel after just three minutes but the Manchester City forward's low cross-shot was blocked by goalkeeper Farinez's foot.
Argentina should have gone in front when German Pezzella ran unmarked onto a flick-on at the back post but he seemed surprised and couldn't react in time with the goal gaping.
There was constant pressure on the Venezuelan backline as Argentina won a succession of corners.
They had 80 percent of possession in the first 10 minutes and sure enough, Venezuela cracked.
Aguero's angled shot was heading well off target as it skidded into a crowd of players, but Martinez instinctively flicked it between his legs, nutmegging an unsighted Farinez.
It was the least Argentina deserved after such a furious start but gradually Venezuela started to settle and get a foothold in the match.
Chances were few and far between but Pezzella got up well to meet a Lionel Messi free-kick, only to head well over the top.
Defenders were proving the most dangerous players on the pitch and Jhon Chancellor rose highest to head over from a corner at the other end.
In first half injury time, Martinez almost had a second put on a plate for him by Marcus Acuna, but Roberto Rosales whisked it off his toe at the back post, four yards from goal as Argentina finished the half with another burst of attacking intent.
- Farinez blunder -
Argentina made another fast start to the second half with Farinez having to punch away a wicked inswinging free-kick from Leandro Paredes, whose slide-rule pass then sent Martinez scampering into the box only to lash his shot against the outside of the post.
Aguero bundled through a number of flimsy challenges but overran the ball and Farinez gathered.
In Darwin Machis, Venezuela had a left winger with the beating of his marker Juan Foyth but the 'Vinotinto' ('Red wine') were unable to get him into the game.
And when they did, Foyth twice got away with robust challenges on the speedy forward inside the box.
The chance Venezuela had been waiting for came on 71 minutes when Tomas Rincon picked out Ronald Hernandez eight yards from goal at an angle, but he rushed his pushed volley and goalkeeper Franco Armani made a smart save.
The game was up three minutes later when Farinez spilled a shot from Aguero that was straight at him, presenting Lo Celso, who had cleverly followed the action from midfield, with a simple tap-in just six minutes after entering the fray.
Even as Venezuela pushed desperately looking for something, Argentina came closer to scoring again a couple of times through substitute Angel Di Maria, earning his 100th cap.