The 24-year-old played in an unconventional midfield role as instructed by the boss as Rotherdam beat Millwall 1-0 in an EFL Championship encounter played on Sunday, August 26.
The Millers scored the only goal of the game when Sean Raggett converted a ball to him by Will Vaulks in the 20th minute.
Semi who played all 90 minutes of the encounter in an advanced position earned praise from his manager after the encounter.
In a report by Warne stated that he could do with more players like Semi who helped tighten up the defence as they held on to their lead.
He said, “Semi was a joke. He could play anywhere for me. He could play up front, on the wing or full-back - I know you might think I’m a bit crazy.
“I could do with signing a few more Semi Ajayi's. He is everywhere for me at the moment.”
The Rotterdam boss also stated that the new could very much feature in a midfield role which offers more risks than in defence.
He said, “I like him there, he looks more confident and he does cover the ground for us and gives us protective cover.
“He looked like he enjoyed it. Being a centre-half if you make an error it's a goal. If you're a centre-mid and you make an error and concede a goal you can blame the two centre-halves behind you. It does give him a bit of freedom.”
The youngster is expected to make his international debut when Nigeria take on Seychelles in an AFCON qualifier or in the friendly against Saudi Arabia.