Of all the Arsenal players taking in the strangely sweet and sour emotions of an elimination after a 3-0 triumph, the one who looked the most crestfallen was Tomas Rosicky, who lay prone on the pitch at the end of it all as if clobbered by a heavyweight's uppercut. The Czech midfielder had put in a particularly inspiring performance. Such was the calibre of his play, once the Arsenal supporters had stopped applauding they were left ruminating the question: where has this little maestro been hiding all these years?

In the past month Rosicky has upped his game to the levels that made him such an exciting signing from Borussia Dortmund when Arsène Wenger did his business nice and early in the summer of 2006, and sealed the deal before the World Cup began in Germany. Rosicky scored two peaches against the USA during that tournament, cementing his reputation as a refined talent. His first season in England was promising enough, but then his career hit the buffers.

The nickname "Rosick-note" sums up a period so bleak there was genuine concern about if, rather than when, he would return. The entire 2008-09 season was wiped out. He did not play a single minute of football. There were whispers that the injury had been misdiagnosed. Others suggested nobody knew how to get to the bottom of it. Whenever Wenger was quizzed about what was wrong or asked for an estimated date for a comeback, the manager was ambivalent. He even referred to it as a "mystery" injury. It seemed everybody was baffled.

In fairness, this kind of obscure extended injury has become worryingly familiar at Arsenal, with Jack Wilshere, Abou Diaby and Thomas Vermaelen all suffering lengthy spells out that seem difficult to explain. Cesc Fábregas, Rosicky's best friend when they were both at Arsenal, was one of his biggest supporters. "I have spent a lot of time with him and I know how he feels," Fábregas said when Rosicky was on the long road back to playing football. "I know what he wants and I have never seen a guy being so committed, so professional and never giving up. If this happened to me I probably wouldn't want to talk to anyone, I would be always down and angry. But he's unbelievable.

"He's the type of player you enjoy playing alongside and as a guy he's amazing. He has been through a lot. I told him to be strong and to keep believing in himself and that he could play football again."

The journey back to the peak of his game has not been easy, though. Through a combination of niggly injuries and struggles to rediscover his rhythm, Rosicky has never started more than 20 games in a season since he came back from his year out. Establishing himself as a guaranteed pick for the first XI has been challenging.

But recent displays have put him to the forefront of Wenger's plans. Most interestingly, in his outstanding displays in Arsenal's past three home games against Blackburn, Tottenham and Milan (won with an aggregate scoreline of 15-3) he has played in his preferred position, as a central schemer.

He has always been a classical playmaker. But rather like Andrey Arshavin, he suffered from Wenger's desire to position players who arrive at the club as an authentic No10 out wide. Neither of them – both experienced internationals who are trusted by their countries to dictate the game from the middle – ever looked at their happiest on the flank.

For much of this campaign Wenger has preferred Aaron Ramsey in the playmaker role. But it is, as far as Rosicky is concerned, a twist of fate that has allowed him to move into the attacking midfield heartland with the young Welshman injured (and looking burned out to boot). Rosicky got this chance to shine, and he has grabbed it. His dribbling and darting across the pitch against Milan rolled back the years. He looked liberated. It was a great team performance, but he was definitely the one who gave Arsenal the impulse to make a game of it.

Robin van Persie defines it as Rosicky being "football clever" and the captain is a nother big admirer. "I just love playing with him because he's so quick in his mind. That's something you can't pick up later in your career. You either have it or you don't."

The "Little Mozart" moniker, one that had not felt particularly appropriate for much of his five-year spell in England, suddenly feels fitting again. Some cynics noted that Rosicky's return to his best coincides conveniently with the time contract renewals come to the fore. A kinder view is that an injury-free player positioned in his most suitable role has made everything click again. Now aged 31, Rosicky has no more time to lose.