That was not luck. Mascherano makes too many well-timed tackles for it to be luck. It was a vital challenge that rescued a situation that could easily have led to Robben beating Romero and heading jubilantly to Rio on Monday, while Mascherano and Messi trudged to Brasilia for tomorrow's third-place play-off.
Many observers believed this World Cup would be about an Argentine Champions League-winning Olympian who plays for Barcelona and whose surname begins with M. But the World Cup's proving as much about Mascherano as Messi, an issue the Germans will have to address urgently at the Maracana.
Messi is Argentina's captain, their talisman, their most creative, feted maestro. His club-mate, Mascherano, is their warrior-in-chief, hounding opponents, reclaiming the ball more than anyone at this tournament, and helping shield a defence, much criticised on arrival, that has not conceded a goal for six hours and 13 minutes. Messi and Mascherano are the light and shade of Argentina, the entertainer and the enforcer.
Capped 104 times, Mascherano is more than a one-dimensional, one-man storm engulfing opponents in possession; he is a highly sophisticated ball-winner, rarely cautioned internationally, and playing more accurate passes than Andrea Pirlo. Memories of him scything down Tal Ben Haim during his Liverpool days, of arguing with referee Steve Bennett, do not feature immediately with the image of Mascherano that now comes to mind.
Mascherano will surely feature in the team of the tournament. He does not need the armband to be Argentina's leader. That beautiful, blue-and-white-striped shirt is a second skin to Mascherano. He is passionate about his country. When Diego Maradona appointed him captain in succession to Javier Zanetti in 2008, the then Argentina coach said he wanted him because he "is the closest to the idea I have about the Argentinian shirt - sweat for it, sacrifice for it". Messi now wears the armband but Mascherano is as committed as ever.
He has never forgotten the pain endured when bowing out of the 2003 world Under-20s in Abu Dhabi. He gets emotional, the tears flowing again after beating Belgium in the quarter-final. It was a huge moment, having failed at that stage in Germany and South Africa. He cried after Maxi Rodriguez thumped his kick past Jasper Cillessen to settle the shoot-out
"Yes," he says when asked whether he cried again, "because I've spent a lot of time waiting for this moment. This is my third World Cup and maybe this is my last one. You never know. But now I am very quiet because we did one job and now we have to do another job. We will see what happens because we are going to play against a big team."
He had rallied the team against Belgium, telling the players that they had to keep going, keep their eyes on the prize of the World Cup so they "don't have to eat s*** any more".
Reminded of this, Mascherano said: "In life, there's a bit of everything. You always have to eat a little bit of dirt."
He is very aware of how he and his teammates march towards destiny. He knows the eyes of a nation rest upon them. "I know the people at home will be happy, because two generations could not see Argentina in the final of a World Cup, they can see us there now so we are happy for that. We will try to give our best. It's been so many years but, well ... now, the eyes of the world are on our country, our flag, returning to a World Cup final."
Now 30, Mascherano was too young to recall Maradona's Argentina defeating West Germany in the 1986 final. "No, but I remember '90, I was very small, but I remember, I remember," he said. He remembers the frustration of that narrow West Germany success in Rome.
That is why Argentina fans are so jubilant, knowing they can avenge that loss with the sweet added bonus of the final being in their rivals' back garden. In Sao Paulo, Argentina fans chanted from one to seven, glorying in Brazil's defeat to Germany.
"We don't think about being in Brazil and that it means more," said Mascherano. "It is a World Cup and this is a chance we have dreamed of. This is the best chance we will have in our lives to lift the trophy and we will try. No, I don't fear losing.
"Obviously if you play against Germany and you leave space for them then it will be very difficult for us. We need to be narrow, we need to be compact. Germany are formidable, they have technique, style. We know that, with space, they're so dangerous."
Mascherano is on a mission, hunting the greatest trophy of all. He has won trophies in Argentina with River Plate and Brazil with Corinthians. He has won the Olympics twice, lost the 2007 Champions League final with Liverpool despite doing brilliantly against Kaka and Clarence Seedorf in Athens. He has won the Champions League and La Liga twice with Barcelona.
He can play centre-half, defensive midfield. He is the type of intelligent, committed, upmarket ball-winner that England crave. Yet when he arrived in England at West Ham, he was kept out of the team by Hayden Mullins, who is now at Notts County. Mascherano is in the World Cup final.
He shrugged. "In football you have to work. You have to keep the mentality. I think when I couldn't play at West Ham I kept my mentality. I went to train every day to be a better player. I didn't have the chance to play in the games in which I wanted to play at West Ham but in football you always have a chance and when I went to Liverpool I had my chance to show my quality."
As here. As in stretching to stop Robben.
