It was a moment that stood to define Oscar's season.
Three days earlier, manager Jose Mourinho had seen his team on the receiving end of a New Year's Day thumping to Tottenham Hotspur. In uncharacteristic fashion, Chelsea had been totally dominated by their London rivals.
Outfought, outthought and outscored, it was the wake-up call Chelsea's season needed.
The expected reaction didn't seem like it would come against Championship opponents, though. Just three of the players who started the game at White Hart Lane were in the lineup against Watford.
Gary Cahill and Cesar Azpilicueta were comfortable in defence, rarely troubled by the visitors' danger man, Troy Deeney.
But that wasn't Chelsea's problem. They lacked any sort of creativity going forward.
There was a lack of urgency, with Oscar the chief culprit for Chelsea's failure to offer any sort of threat themselves.
Midway through the first half, Oscar went down after a challenge, seemingly injured on the sideline.
Within seconds, he was back on his feet, the sound of his manager's voice ringing in his ear. Mourinho wasn't happy with Chelsea's performance, especially that of his playmaker. As he rushed over to him, forcing Oscar to his feet, that much was clear.
We couldn't hear what was said, yet it didn't matter. Whether he spoke in English or Portuguese, everyone inside Stamford Bridge understood Mourinho's message.
At half-time, Oscar was replaced by Willian. Within 13 minutes, Chelsea were 1-0 up.
The goalscorer? You've guessed it: Oscar's replacement.
Chelsea would go on to win the game 3-0.
It must have been frustrating for the player to see Willian score that important goal, but it was much more so for those fans in attendance.
Too often, Oscar has left it to his team-mates to do the job he is there for, and it was happening again. Almost like clockwork, the traditional half-season dip had started in earnest.
Up to that point, Oscar had been so influential for Chelsea. Mourinho's side was racing clear in the Premier League title race, and it was down to those combinations we bore witness to in the attacking third.
Eden Hazard, Diego Costa, Cesc Fabregas and Oscar were the key players. With the singing of "Auld Lang Syne," that quartet quickly became a trio, and we didn't see much from Oscar for the rest of the campaign.
There was the odd moment of brilliance, although that isn't good enough.
Oscar frustrates so much because we know how good he can be. When at his best, there aren't many players like him in world football.
The Brazilian gives options in attack and helps Chelsea maintain a solid defensive base. The sight of him pressing in the final third excites, showing his hunger to win and work for his team-mates.
It ensures Mourinho can implement his tactics properly, creating the sort of team that can lead the Premier League table from the start of a season right through to the end.
When those levels drop, however, Oscar's value tanks. Considerably. He's an altogether different player—one at odds with the man we have seen previously. Post-Christmas, it's a wonder how he ever made it to Chelsea at all.
The theory is that it's fatigue. Oscar's not had a summer off at Chelsea until this year—he missed the Copa America through injury—so the hope is that he will be better for it in 2015/16.
Here's the point, though: Oscar has been a Chelsea player for three seasons, and we're still asking the same questions about him.
There are still doubts in areas where there shouldn't be.
Can he last a season? Is the 23-year-old the long-term solution at No. 10? Is he actually good enough?
Oscar should have answered those questions a long time ago. Instead, here we are as Chelsea return for a pre-season to defend their championship crown, and we're none the wiser as to whether or not they're sufficiently stocked in the attacking midfield.
If Oscar performs to his best all season, it's a categorical thumbs-up. If not, Chelsea have problems.
It shouldn't come down to that. Not now.
Garry Hayes is Bleacher Report's lead Chelsea correspondent. All quotes were obtained firsthand unless otherwise noted. Follow him on Twitter @garryhayes.