Sergio Aguero scored a brilliant near-post header as tournament favourites Argentina defeated defending champions Uruguay at the Copa America.
The Manchester City striker converted Pablo Zabaleta's cross after the break.
Argentina were held by Paraguay in their opening game but now lead Group B after a deserved victory in a tense and, at times, bad-tempered game.
However, Diego Rolan should have equalised for Uruguay but blazed over from eight yards.
It also took a good block late on to keep out a header from Uruguay skipper Diego Godin, while Hull City's Adel Hernandez had a side-foot effort brilliantly clawed out by Sergio Romero.
It was a reminder to Argentina of the fragility of their lead but they managed to see the game out to claim the 82nd victory over their South American neighbours.
Argentina now face the pointless Jamaica in their final group game after the Caribbean side - invited guests playing for the first time at the tournament - lost 1-0 to Paraguay in their second group game.
The only goal of that game came through Edgar Benitez after a terrible error from Jamaica goalkeeper Duwayne Kerr, who charged 25 yards from his goal but only succeeded in heading the ball into his opponent's path.
In La Serena, Argentina and Uruguay contested a tight and uncompromising contest, as might be expected between two fierce rivals meeting for the 178th time.
Argentina - with Aguero, Lionel Messi and Angel Di Maria in their starting XI - dominated possession and territory while Uruguay, looking to build on their opening win over Jamaica, were compact, stubborn and wily in defence.
There were precious few openings during the first half, although Uruguay's Rolan should have done better with a header that skimmed wide after his team showed the threat they posed on the counter attack.
There was a frustrated look to Argentina as they trooped off at the break, while coach Gerardo Martino had already been sent to the stands for arguing with the officials.
But that changed 10 minutes after the restart with Aguero's brilliant and brave near-post header under huge pressure from Jose Maria Gimenez.
The game opened up after that and became increasingly fractious, with an unnecessary lunge at the opposition goalkeeper from Manchester United defender Marcos Rojo sparking a penalty-box melee, while Egidio Arevalo Rios and Messi later briefly squared up.
And although Uruguay did create chances to equalise, Argentina almost doubled their advantage when a low strike from Messi drew a good save from Fernando Muslera.
It leaves Argentina with four points from two games, while Paraguay have four and Uruguay three ahead of their meeting on Saturday.