As well as netting a brace, the 24-year-old Belgium international - signed from Olympiakos earlier this month - also set up goals for Leon Osman and Victor Anichebe in the first half at Goodison Park, before Magaye Gueye's second-half volley completed the Barclays Premier League side's rout of their npower League One opponents.
Reflecting on Mirallas' exploits, Round told www.evertonfc.com: "Kevin gave us a cameo of what he's about with his speed, his movement and his finishing. He showed why he was one of the top goalscorers in Greece. That is why we have got him at the club."
He added: "He tired quite badly in the second half but we expected that. He missed quite a chunk of pre-season with a knee injury. He's not really up to speed yet but he is getting there."
The result meant Everton's good start to the season continued, the Toffees having gone into the match off the back of league wins over Manchester United and Aston Villa.
Manager David Moyes opted to make six changes for the contest from the first XI that started the 3-1 triumph at Villa Park on Saturday, but the Merseysiders had no trouble finding their rhythm against Orient and Round was keen to praise the contributions of the incoming personnel and the way the team had approached their task overall.
He said: "That is the beauty of our squad at the moment. Having everyone fit and with the quality we have got within our 16 or 17 players, we could make those changes and still be competitive. Credit to the guys who came in.
"Performance always follows attitude - if your attitude is right, you get the performance right. That was a really pleasing aspect. I don't think I've ever had to question the attitude of an Everton team ever, and you saw tonight that they meant business right from the off."
The only potential negative for Everton was that skipper Phil Neville limped off towards the end, although Round revealed afterwards that the injury did not appear to be too serious.
Asked about Neville's condition, Round said: "He had a bit of a tight hamstring and cramped up. We weren't going to take any risks so we took him off straight away and it looks like he'll be okay."
Source: PA
Source: PA