Having concluded, in his half-term report, that the team with the deepest reserves of mental strength would win the title, Arsène Wenger watched his Arsenal team withstand Birmingham's efforts to test their courage and ultimately impose their own methodology where once, perhaps, they would have been found wanting.
It was by no means a brutal performance from Birmingham, who are better and classier than to resort to such tactics as a means to an end. But there were a couple of challenges – a robustly committed tackle on Cesc Fabregas by Roger Johnson in the first eight minutes and, later, a stamp (spotted by the cameras rather than the officials) by Lee Bowyer on Bacary Sagna – that might have unnerved a less mature Arsenal.
But instead of wilting, Arsenal built on the foundation of a free-kick from Robin van Persie, deflected past Ben Foster, after 13 minutes, retained their belief in the quality of their football and became stronger. It helped that three of Birmingham's back four had to play most of the second half on yellow cards but it was difficult not to admireArsenal's technical gifts, not least those displayed by Samir Nasri, who wrote another uplifting chapter in his outstanding season, scoring his 13th goal and setting up another.
"We were prepared today to face physical challenges and prepared to not lose our game, to be calm and remain focused on the way we play," Wenger said. "We had chances in the first half and I believe we grew stronger and in the second half played an outstanding game. I would rather talk about my team's performance than any individual challenges. I am convinced the way we played today will strengthen the belief in the squad."
Indeed, after the squandering of points at Wigan, where Wenger gambled badly with a much-changed team, this was more like the superiority required from potential champions. Where Manchester United could secure only a point, Arsenal became the first visiting team to score three goals here in more than two years.
This time there was no gambling. Birmingham may be in the bottom three but Wenger judged that a home record that includes a victory over Chelsea and points won against Tottenham and United deserved proper respect. After the eight changes he made against Wigan in midweek, he started with the same team that had beaten Chelsea so impressively two days earlier.
The home side, unchanged from the side that clawed back a late equaliser against United last Tuesday, offered strong and committed resistance, as might be expected of a team previously beaten only once at home in the League since September 2009.
Arsenal's half-time lead owed something to referee Peter Walton, who awarded a generous free-kick against Scott Dann, from which Van Persie scored, and then failed to award a penalty when Van Persie, at the other end, touched the ball with his arm before a Johnson header was cleared.
"How the referee has not seen that, I don't know," McLeish said. "Normally the dug-out is a terrible vantage point but we could see clearly that he used an arm to control the ball. Whatever the result, Arsenal would have been the classier side. But goals change games."
Van Persie missed two chances to extend Arsenal's lead and perhaps they were the more significant incidents, portents of what was to come. By the 66th minute, they were three goals to the good, home and hosed.
Nasri scored the second, driven from just inside the area, in the face of a retreating Birmingham defence after a one-two with Fabregas, with whom he combined again with intricate interchanges to set up what would have been an exquisite goal had it ended with a clean finish. Foster made his second brave save of the second half, the first having denied Nasri, when Fabregas released a close-range shot but the ball hit Dann and Johnson too before rolling across the line.
Referee: Peter Walton
Man of the match: Nasri