"I enjoyed playing but when I damaged my cruciate ligament I came to the realisation I couldn't play any higher so I took up coaching," says the 31-year-old Central Football administrator.
Birnie is assistant coach of the Young Football Ferns to former Czech Republic international Jitka Klimkova, who has been based in Auckland for the past 12 months before they jet off to Costa Rica next month to compete in the Fifa Under-17 girls' World Cup.
Four players from the Central Football region - Sarah Morton (Maycenvale), Sophie Hoar (Napier Marist), Ashley Arquette (ex-Maycenvale) and Karan Ingram (Palmerston North) - will feel the tension this weekend as they wait for the 35-member squad to be culled to 21 when New Zealand Football announces the team on Monday.
Versatile Morton is a winger/fullback, Arquette is a midfielder who has just returned from Christchurch where she was a member of the Asia-Pacific Academy for the past two years and Ingram is a centreback.
Goalkeeper Hoar is vying for a berth among four hopefuls but only three will make it.
The squad competed in Australia last August to gain experience where they lost two games and won one.
Sticking to a core group, the squad took a few different players this month to play three games in the United States.
They lost all their games - 5-0 to Japan, 2-0 to the US and 5-1 to China - at the Stub Hub, the home venue of the LA Galaxy Soccer Club.
"To put it in context, 95 per cent of our players were making their international debut so to play two out of three top-ranked teams in the world was a huge ask," says Birnie who returned home with Morton on Wednesday.
Needless to say, the Kiwi players have their work cut out before they jet off on March 7 to play Paraguay (March 16), Spain (March 19) and Japan (March 23) in their pool.
"For some of the girls it was their first taste of international football and what it's all about and the opportunity to play the world's best." The bigger picture is to expose the players to a basic possession-based philosophy where they can make good decisions under pressure across the park.
"Coming in at the age of 17 they get a simplified version of what the Football Ferns are doing and how they will fit in."
Morton, 17, of Hastings Girls' High School, realises she has to run a lot more so fitness is a priority for the fifth-former who found the left wing more challenging than the right.
"I enjoyed both positions but I think the left wing taught me more," says the teenager from Central Hawke's Bay who also has no qualms about defending.
Staying strong on the ball and having the right mental fortitude also stuck out for her.
"We went into the [Galaxy] stadium where we saw a few [first-div] players training but we didn't say anything to them," says Morton, who will be in school on Monday but will rely on her parents to inform her of selection through the office staff.
For Birnie, having a vision and meticulously working his way up from Akina is yielding dividends.
It is a testimony to his diligence and making the most of what NZ Football's system offers in obtaining coaching badges for the past decade. The former adroit midfielder/striker is now a senior level three qualified coach, the maximum level one can attain in the country.
He harbours no regrets about not coaching overseas, something he did as a player in his prime when he turned down an invite from the Prince of Brunei in the summer of 2005-06, after injuring his knee two days before jetting off to the Southeast Asian nation.
His other biggest mistake was not going to Auckland when selected for the under-17 World Cup team.
"If I was going overseas I would have done it long time ago," he says of coaching.
"If the opportunity arises for a head coaching role I'll take it but I'm always better off coaching and having a family life," he says as he and Michelle Gillespie embark on the exciting and challenging journey of parenthood.
He is enjoying honing his coaching prowess with Klimkova as well.
Birnie impresses, though, he couldn't have done it without the help of others.
Brett Angel, of Central Football, has been his mentor and Lotto's sponsorship is vital.
"I've learned heaps from Brett."
