It was a lot closer than most expected the scoreline to be, but McKellar warned the trip to Japan will no longer be an automatic win for teams in the Super Rugby season.
"It is relief. I thought there were some really good passages from us in attack, but in the first 20 minutes we didn't stick to our plan," McKellar said after his first game in charge.
"We just need to understand that we're changing how we play, it's not going to be perfect overnight. I'm really proud of the effort, I think we showed a lot of resilience to grind out that win against a Sunwolves team that's going to win a lot of games this year."
The overriding good news for the Brumbies is that they started their season with a win, even if it wasn't the bonus-point triumph most people tipped them to get.
The challenge will be ensuring they don't fall behind like they did against the Sunwolves, where they trailed 14-3 and then 19-8 just before half-time.
Teenage flanker Rob Valetini is facing a stint on the sideline after injuring the medial ligament in his knee, but the Brumbies won't know the extent of the damage until they return to Canberra on Sunday.
If Valetini is ruled out for an extended period, Lachlan McCaffrey looms as the man to fill the hole after he made an eye-catching return in his first Super Rugby game since 2014.
Wallabies prop Scott Sio could also be available for a clash against the Queensland Reds in Brisbane on Friday night after missing the opening round with a calf injury, and Lolo Fakaosilea will come into back-row contention.
But the first game of the season almost went pear-shaped as the howling Tokyo crowd lifted the home side and helped it charge to a lead.
The Sunwolves scored the first three tries - two to "Tongan Godzilla" Hosea Saumaki - to open up an 11-point lead before the Brumbies even got out of first gear.
By the time the visitors eventually found their feet, they were in danger of being blown off the park in what would have been a monumental upset.
McCaffrey, Kyle Godwin, Tevita Kuridrani, Josh Mann-Rea and Tom Banks scored tries for the Brumbies, while they limited the Sunwolves to just six points in the second half.
"I take it as a good win, that was a tough match," said Brumbies co-captain Sam Carter.
"They tested us and we had to stick to our structures. The pleasing thing is we did that and got a hard fought win.
"We're not going to hold our heads down. That was a good start to the season, we'll recoup and move forward. There was a bit of panic for a bit, they were coming at us. For us, we adapted and showed great positivity."
The Brumbies blooded five new faces in the match - teenager Rob Valetini, Isi Naisarani, Richie Arnold, Chance Peni and Matt Lucas.
Naisarani lived up to his billing as a future Wallaby, easily the stand out performer for the Brumbies in a scrappy clash.
McCaffrey came on to replace Valetini after just 20 minutes and showed his value, scoring a try of his own, setting up another and being a work-horse around the field.
Christian Lealiifano was solid in his first starting game for the Brumbies in almost two years after a battle against leukaemia, and he got rid of any nerves when he slotted the opening points via an early penalty.
"The Sunwolves played well ... they were very good at spreading the ball and challenged us there, we had to adapt and I think our team did that OK in the second half. There's plenty to work on," Lealiifano said.
AT A GLANCE
Super Rugby: ACT BRUMBIES 32 (Lachlan McCaffrey, Kyle Godwin, Tevita Kuridrani, Josh Mann-Rea, Tom Banks tries; Christian Lealiifano penalty, 2 conversions) bt JAPAN SUNWOLVES 25 (Hosea Saumaki 2, Timothy Lafaele tries; Ryoto Nakamura, Hayden Parker conversions; Hayden Parker 2 penalties) at Prince Chichibu Memorial Stadium, Tokyo, on Saturday. Referee: Paul Williams.
Morning & Afternoon Newsletter
Chris Dutton is a sports reporter at The Canberra Times.
Brumbies Super Rugby History
The Brumbies’ (formerly the ‘ACT Brumbies’) are a Super rugby union team based in Canberra, Australia and named for the wild horses which inhabit Canberra’s hinterland.
The Brumbies were formed in 1996 to provide a third Australian team for the newly-formed Super 12 (now Super Rugby) competition. It was predicted that the Brumbies, made up of so called ‘rejects’ – players not wanted by other two teams – would crash very, very quickly.
Since then, they have enjoyed more success than the other Australian teams (the New South Wales Waratahs, Queensland Reds and the Western Force), reaching five finals and winning two, being the only Australian team to have done so.
They defeated South Africa’s Sharks 36-6 in 2001 and won the competition for the second time on May 22, 2004 with a 47-38 victory over the Crusaders of New Zealand’s South Island.
The team plays at Canberra Stadium (formerly known as Bruce Stadium) in Canberra and are coached by Jake White and assistant Laurie Fisher.
Previous Brumbies coaches include Rod Macqueen and Eddie Jones, who both went on to coach the Wallabies, while Jones and David Nucifora were at the helm to help guide the side to their Super 12 Championships in 2001 and 2004, respectively.
Famous Brumbies players have included George Smith, widely regarded as one of the best openside flankers in the world, Mark Gerrard, Mark Chisholm, Clyde Rathbone, Guy Shepherdson, Stirling Mortlock and George Gregan.
The Brumbies have traditionally formed the backbone of the Wallabies, with 10 members selected for the 30-man Australian squad for the 2007 Rugby World Cup.
The Brumbies mascot is Brumby Jack and is pictured on the right.
Super 15 postions
2015 .. 6th Lost in Semi-final to Hurricanes
2014 ..4th Lost in Semi-final to Waratahs
2013 .. 2nd Lost in final to Chiefs
2012 .. 7th
2011 .. 13th
Super 14 positions
2010 .. 6th
2009 .. 7th
2008 .. 9th
2007 .. 5th
2006 .. 6th
Super 12 positions
2005 .. 5th
2004 .. 1st .. (defeated Crusaders in final)
2003 .. 4th .. (lost semi-final to Blues)
2002 .. 2nd .. (lost final to Crusaders)
2001 .. 1st .. (defeated Sharks in final)
2000 .. 2nd .. (lost final to Crusaders)
1999 .. 5th
1998 .. 10th
1997 .. 2nd .. (lost final to Auckland Blues)
1996 .. 5th