Amateur player Mifsud saved Australia from defeat as he recorded singles victories over Tony Drago and Alex Borg in their 3-2 victory over Malta.
The success, along with Australia's 4-1 triumph over Thailand 1 on Monday, leaves Australia top of the table and Robertson was delighted with Mifsud's form.
"Steve hasn't played under this kind of pressure and it's good for him to produce the goods when it matters," said Robertson.
"He really did well. I lost the first frame and you don't want to go 2-0 down in this format but if it wasn't for Steve we would've lost the match.
"He was under pressure twice and won twice. He beat James Wattana last night and has now beaten Tony Drago and Alex Borg today.
"Steve and I practised regularly when I was back home but we've known each other for 16 years and both of our families knows each other.
"It's nice to play with someone you've known for such a long time and it's fantastic to be representing your country. In our country it means a bit more to play for your country than in other places and they wouldn't get as much coverage if they won as we would get.
"We can't get too far ahead of ourselves but we've got off to the perfect start and this is the toughest one of the groups."
Mifsud, 39, who will also be in action later this month in the Australian Goldfields Open immediately after this event, was delighted to get this opportunity.
"I play amateur snooker in Australia so it's a privilege to play with Neil and it's very exciting," said Mifsud. "I'm just happy to be out there so it's nice to be knocking a few balls in.
"I never imagined that I would be playing in a professional tournament like this and to be here with these players. There are some very talented players here from lots of different countries.
"As a kid I remember watching Tony Drago as my parents were born in Malta, although I was born in Australia, so I have a connection with Malta. Tony Drago inspired me to play snooker as a kid so this was a really big match for me."
Robertson believed the World Cup was vital for the development of snooker.
"Since Barry (Hearn) has come in he has really expanded the game and wants it to be a global game - the World Cup is the perfect way for that to happen," added Robertson.
"Hopefully there will be a good mix of international nations from everywhere in the quarter-finals."