The Spaniard was appointed into the Bramall Lane hotseat following the surprise sacking of Chris Wilder after the Blades’ play-off final defeat, but his stint could not have begun any worse.
Scott Twine’s double and goals from Ross McCrorie and Anis Mehmeti ensured Gerard Struber’s first game in charge of the Robins was a much more enjoyable affair.
Tyrese Campbell had levelled for the Blades but this performance will raise big questions about their promotion credentials this term.
City were back at Bramall Lane, where they left crestfallen after their play-off semi-final defeat in May, but the emotions were entirely different.
It was just 89 days ago that the Blades spanked the Robins to book their place at Wembley with a 6-0 semi-final aggregate win, but they found life much tougher this time.
They fell behind in the fifth minute as Twine converted a trademark free-kick, whipping a 25-yard effort over the wall which left Blades goalkeeper Michael Cooper rooted to the floor.
It was almost 2-0 soon after as Twine danced through the Blades defence and looked primed to score until Femi Seriki made a vital block.
That proved important as the Blades were level in the 14th minute when they scored an excellent equaliser.
Callum O’Hare threaded an incisive pass through to Campbell, who thrashed home from 12 yards.
The Blades had their tails up and could easily have gone in front but Louis Barry had an effort deflected just wide, City defender Jason Knight almost scored an own goal and Harrison Burrows’ drilled effort was beaten away by Radek Vitek.
But, in a game where neither defence looked solid, it was City that regained the lead in the 26th minute.
Twine received the ball in the middle and found McCrorie, who drilled into the bottom corner.
Things got even better after the break as they extended their lead just 36 seconds into the second half when Emil Jakobsen got in down the right and teed up Mehmeti to sweep home.
It was 4-1 in the 51st minute after Rhys Norrington-Davies’ pass was intercepted by McCrorie and he passed to Twine, whose effort deflected off Tyler Bindon and into the net.
Jakobsen should have made it five but he blazed over from close range when a loose ball fell to him.
Tom Cannon and Sydie Peck were both denied as the Blades tried to reduce their arrears but they were booed by an unforgiving home crowd.