It was Jose Mourinho. The Chelsea manager, together with his coach Andre Villas, had watched Duff produce a performance of extraordinary skill, determination and aggression against Mourinho's home country and one of the world's highest-ranked nations. After Ireland's 1-0 victory, Mourinho had hugged Duff before making sure he got into the car and was whisked away to Dublin airport - along with Paulo Ferreira and Tiago - for a private jet back to London. The vehicle's upholstery was probably lined with cotton wool, such is Duff's value right now.
It was different for player and manager not so long ago. Last September Mourinho attended the Republic of Ireland's World Cup qualifier against Cyprus in Dublin, and left without even speaking to Duff. That upset the 25-year-old, who feared at that time that Mourinho did not want him. Having seen Arjen Robben arrive at Chelsea, Duff thought there would not be room for both of them. When he spoke in Switzerland, for another qualifier a few days later, there was anxiety in his eyes.
Against Portugal on Wednesday night, there was an edge to his performance. No one had seen Duff play so fiercely. After just four minutes he tussled with Cristiano Ronaldo and there was an angry exchange. It seemed so incongruous. Just after the hour Duff tripped up the Manchester United winger and was booked before rapidly being clattered himself and substituted. But before that he had played brilliantly. Mourinho, to his credit, has made Duff a better, harder, fitter player.
Friends of Duff indicated yesterday that it was just his determination to do well in his 50th international with all his family watching. He loves playing for Ireland and it shows. He also loves playing for Chelsea, is happy, and settled. Mourinho may not have had him in his plans when he arrived - there has been continued speculation over wingers such as Joaquin - but he has revised his opinion.
Barcelona, Chelsea's opponents in the Champions' League, would certainly be interested if Mourinho changed his mind again. But the Chelsea manager should also remember that Duff has been Roman Abramovich's favourite player. And in the absence of the injured Robben, he needs him more than ever.
As do Ireland. Their record under Kerr is extraordinary - 25 games played, just two lost and only three goals conceded in the last 12 matches. Confidence is high and competition for places is strong. But there is also a little anxiety. After all, friendly victories against Portugal or the Czech Republic matter less than next month's vital World Cup qualifier away to Israel. Victory there and the World Cup will surely be Duff's next stage.