Antonio Conte knew. He didn’t need to see Andres Iniesta pick out Lionel Messi. He didn’t need to see the ball find Messi’s famed left foot 15 yards from goal. He didn’t need to see the net bulge. His hands were already on his head.

He, and a good portion of his players, and tens of thousands of Chelsea fans knew that they were witnessing the moment that could haunt them for weeks, and perhaps months, to come.

They had, for the most part, executed their plan. And Willian had provided the moment of magic that seemingly ensured their execution would pay off. But one wayward Andreas Christensen pass, and one split second of Cesc Fabregas hesitation, and one late, ill-advised gamble from Cesar Azpilicueta undid it all.

Chelsea was on its way to Barcelona with a 1-0 advantage – a scoreline that would have been both favorable and deserved. In a matter of seven seconds, the Blues went from an advantageous position to troubling one ahead of their Champions League round of 16 second leg in Catalonia.

“Overall, fantastic performance,” Fabregas said afterward, succinctly summing up the dynamics of the 90 minutes. “In the end … shame.”

Chelsea had conceded possession, and at times territory, throughout the match. But it had conjured the better chances. Willian struck both posts in the first half from outside the area.

He, Pedro and Eden Hazard, drafted by Conte as a striker-less attacking trident, connected with first-time flicks and threatened Barca on the break.

At times they were pinned back, called on to help clog Barcelona passing lanes and restrict Messi’s space. When they were, they became disconnected, unable to provide outlets. But such spells are par for the course against Barca, and Chelsea limited their length.

The La Liga leaders had much of the ball, but nothing more than a miscued Paulinho header to show for their control in the first half. The Brazilian midfield played almost as an inside forward off the right, joining Suarez up top as Messi floated underneath. But with Chelsea wing backs neutralizing overlapping Barca full backs, the back three rotating well and N’Golo Kante patrolling the middle, the Blues were rarely stretched.

Willian then gave them a lead after the hour mark with a clever finish from the top of the box:

The goal wasn’t exactly emblematic of Chelsea’s threat, nor of its approach. It wasn’t even necessarily a clever, premeditated set-piece routine. Barca simply failed to account for Willian at the top of the box. But it was certainly a just reward for all the work that Chelsea had put in, both in preparation for Tuesday night and over the opening 60-plus minutes.

The Blues reined in some of their attacking impetus after the goal, but did still have counterattacking lanes to stream into. On one occasion, Willian nearly picked out a late run from Kante, but Jordi Alba had raced back to deny Chelsea great look at a second.

The visitors showed very few signs of getting their crucial away goal until … well, until they got it. They pounced on the errant pass, Iniesta keeping his composure and teeing up Messi for the Argentine’s first goal against Chelsea. Suddenly, Chelsea’s masterpiece had come undone.

The Blues, of course, are by no means done in two-leg series. They’ll head to Spain buoyed by their performance.

But, as Fabregas said afterward, “1-0 would have been a fantastic result. Now you give them a big chance, because at the Nou Camp they are very strong.”

Tuesday’s other Champions League first leg

Bayern Munich 5-0 Besiktas

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Henry Bushnell covers global soccer, and occasionally other ball games, for Yahoo Sports. Have a tip? Question? Comment? Email him at henrydbushnell@gmail.com or follow him on Twitter @HenryBushnell.