Lewis Grabban's opener for Sunderland was a result of Archer feebly slapping the ball away from goal, handing the former Bournemouth striker a simple tap-in.
Luckily for Archer, though, his opposite number endured a similarly woeful afternoon.
George Saville converted Millwall's equaliser four minutes later, after summer arrival Ruiter let the ball squirm through his legs.
Saville followed up with another well-taken free-kick in the 20th minute which the Dutch goalkeeper tamely parried into his own net.
But there was still chance for Archer to cap off his own miserable afternoon with a terrible attempt to push clear Adam Matthews' cross... that ended up sailing in.
To their credit, both goalkeepers also pulled off some smart saves in the game – but in the moments that mattered, there were few excuses to hide behind.
"I don't think you will see many matches where there are so many mistakes by the goalkeepers," Sunderland caretaker manager Robbie Stockdale told the Sunderland Echo.
"Nobody means to make a mistake but when a goalkeeper makes them, that is your last line of defence and usually it goes in.
"I didn't make a point of bringing it up [with Ruiter at half-time]. When you make a mistake like that it is obvious for everyone to see."
See also...
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Has Brentford's Neal Maupay produced the miss of the season? (Answer: yes)
