It was not the shot against the post, or the offside goal, or the attempt that hit Anthony Elanga on the goal line that epitomised Cristiano Ronaldo's demoralising day, but a free-kick.
In the 38th minute, Ronaldo walked away from a free hit 25 yards from goal. Rio Ferdinand joked back in September Ronaldo should not be allowed to have first dibs on set-pieces. Against Watford, Ronaldo did not even protest as Alex Telles lined up to swing a harmless shot wide.
When the final beep sounded, Ronaldo looked broken. At Old Trafford, the tunnel is located in the south-west corner, rather than on the halfway line as it is at most grounds, so there was no quick getaway. Ronaldo lingered, maybe wondering what he had got himself in for. Maybe wondering what has happened to him.
He sheepishly applauded the Stretford End, his head bowed. That was an admission of guilt. Ronaldo was a missed penalty away from the full profligate set on another afternoon United fired blanks.
A colleague in the press room quipped prior to kick-off Ronaldo resembles a reclusive Bruce Wayne in The Dark Knight Rises before he suits up again. Batman eventually gets broken. Ronaldo looks broken.
Ronaldo has been caught offside 25 times in the Premier League this season - more than any other player. In his five domestic starts in February, he was caught ahead of the last man nine times.
Scan through the list of the most flagged players and there is a trend: Ronaldo, Raul Jimenez, Chris Wood, Jamie Vardy, Callum Wilson and Michail Antonio are all in their 30s and all in need of a head-start. Ivan Toney and Jarrod Bowen, both 25, have spent the bulk of their careers in the Football League.
Ronaldo tops the chart with 25 offsides. Sir Alex Ferguson once said Filippo Inzaghi was born offside and Ronaldo's passport is in danger of listing the same birthplace.
For those who had the privilege of watching Ronaldo during his formative years at United, he is cursing the heavens as much as when he was a teenager. Ronaldo pinged the woodwork with luckless regularity- in his first two seasons, yet you knew the kid would come good, very good.
Nobody is expecting a 40 or 50-goal haul from the game's greatest goalscorer in his twilight years. Ronaldo is operating in the most demanding league and he still struck 14 goals in his first 20 games back at United - all of them in the Premier League and Champions League. Almost all of them secured points.
There is the mitigation of his current lean spell of one in the last 10 coinciding with a hip injury that forced him to miss two games in January and Edinson Cavani crying off as soon as the weather turned. United had seven games in 22 days in February and Cavani was available for one of them.
United fans have limited their serenading of Cavani and his lyric might as well be changed to 'first name's Edinson and it's another injury'. Just like last year, Cavani did not play whatsoever in the second half of February and he failed to make the matchday squad after all four rounds of international fixtures this term.
When Cavani crosses the white line, his commitment is unquestionable. Until he charged after the ball with the game deadlocked at 1-1 against Villarreal, preventing a goal kick had never gone viral. Away from the pitch, Cavani currently appears about as committed to attending United games as absentee landlord Joel Glazer.
The circumstances of re-signing Ronaldo were troubling but it is just as well United did. Cavani has missed 22 out of a possible 37 games and scored twice in his second season. United cannot say they weren't warned as Ole Gunnar Solskjaer became frustrated with Cavani's tendency to offer a second opinion on his fitness and Ralf Rangnick has not concealed the fact Cavani's say is final.
Ronaldo is a victim of typically poor planning. United have two goalscorers with a combined age of 72 and one is a fair-weather player. It is not a coincidence Cavani's purple patch last year started in April and ended in May.
The goalscoring issue is so acute Bruno Fernandes has arguably been more wasteful this month in February. His misses against Watford were worse than Ronaldo's and Fernandes was similarly culpable in the FA Cup ejection by Middlesbrough.
Beyond the Latino contingent, Marcus Rashford - never a centre forward - has mustered 12 club goals in 14 months, roughly how long he has been out of form. Anthony Elanga has shown promise but is callow. No sensible matchgoer ever leaves Old Trafford rueing Anthony Martial's absence.
United's impotence is as much mental as it is technical. The dominant halves of Boro, Burnley and Southampton are so current they must have played on the mind as Fernandes tensed up and Ronaldo edged ahead of the final man at the Scoreboard End on Saturday.
The only minimum four-goal hauls United have registered this season have been against the tactical anarchists of Leeds and Steve Bruce's sinking Newcastle ship. Under Rangnick, they have scored twice in four games out of 17.
