Until Yekta Kurtulus came on for Izet Hajrovic after half an hour, there was a serious possibility that Galatasaray, like so many other home teams in the last 16 of this season's Champions League, would be swept away.
Every Chelsea counter-attack seemed to threaten, the game falling into a pattern of tentative Galatasaray possession followed by three or four blue shirts bearing down on exposed defenders.
The high line played by Roberto Mancini, it seemed generally agreed, was a major tactical blunder.
Perhaps it was, but there is need to distinguish between the plan and its execution. The logic of the high line is to squeeze play, to compress the area in which an opponent is playing, to make them hurry in their passing and so make it easier to regain possession quickly.
The risk is the space that is left behind the back four. The higher the press, the bigger the space and the easier it is for an opponent to measure a pass into that area for a runner.
There are two ways of alleviating that danger. The first is to have a goalkeeper who sweeps outside his box, filling the space and looking to react first to intercept any through ball. Fernando Muslera, the Galatasaray goalkeeper, never looked comfortable doing that, his evening characterised by that nervy moment early on when he came from his box and cleared the ball straight to Willian before reacting sharply to make an unorthodox save by deflecting the Brazilian's first-time shot wide with his head.
The other, even more fundamental way, is for the midfield to press the opposition in possession. Given that the whole point of the high line is to facilitate the press, that is essential. And it was in that facet that Galatasaray were found so wanting. Again and again, Chelsea midfielders had time to receive the ball, look up and calibrate a pass into the space behind the back four. The intensity necessary to unsettle them simply wasn't there.
Galatasaray 0-1 Chelsea HT: Top rated players - Torres (7.6), Azpilicueta (7.2), Balta (6.9), Chedjou / Cech (6.8) #UCL— WhoScored.com (@WhoScored) February 26, 2014
Mancini had taken a risk in playing an attacking 4-4-2 with two attacking wide players, but he was still entitled to expect them to do their job with rather more urgency and efficiency than they did.
Hajrovic is a gifted young player, and his goal as a substitute in Slovakia was a major factor in Bosnia-Herzegovina's qualification for the World Cup, but it's telling that when he went off, according to stats on whoscored.com, he hadn't made a single tackle or interception.
It's not a coincidence that the Chelsea goal, scored by Fernando Torres, came from a surge by their left-back Cesar Azpilicueta, who was able to break forwards unchecked by his direct opponent.
Frankly, Galatasaray were fortunate only to be one down when Mancini finally decided to change approach. Kurtulus's arrival meant Buruk Yilmaz pulling wide and a shift to a 4-1-4-1. The extra central midfielder gave Galatasaray more bite in the middle and, although Torres remained a threat on the break, thanks in part to the lack of pace of Hakan Balta and then Semih Kaya, who replaced him at half-time, Chelsea were nowhere near as rampant as they had been.
Although the Galatasaray equaliser was the result of some poor marking from a corner, it said much for the way the game had turned and the atmosphere in the stadium that Jose Mourinho reacted by bringing on John Obi Mikel immediately.
Another manager might have been tempted to chase the game in frustration at having failed to capitalise on their early dominance, but Mourinho saw the momentum had shifted and looked to close the game down, something at which he was extremely successful.
The final quarter of the game may have been largely eventless, but it means Chelsea go into the second leg with a clear advantage.