Balazs is also the first Canadian to gain a spot in an Olympic marathon swimming race. Canada had no entries in 2008 when open water swimming made its Olympic debut in Beijing.
"Right now, I don't think it's hit me yet that I'm actually going to the Olympic Games," said the 21-year-old Balazs. "It's something that I've wanted for so long. The biggest challenge for me this week was actually believing in myself that I could actually do it."
The race was held in frigid waters on Setubal Bay and Balazs was exhausted as she approached the sixth and final lap. She was 13th after five laps after clocking first, fourth, fifth and fourth in the first four laps respectively.
"I didn't really know where I was," said the two-time world championship team member. "I did a really good last turn, though, and realized there wasn't that many swimmers ahead of me."
Haley Anderson of the U.S., won the gold medal in one hour 44 minutes 30.6 seconds. Eva Risztov of Hungary took second in 1:44:32.0 and her compatriot Anna Olasz was third in 1:44:36.8.
Balazs finished in 1:44:38.8. The top-nine swimmers, a limit of one per nation, earned their ticket to London.
Nadine Williams of Edmonton was 11th in 1:44:48.8.
The men's 10-kilometre marathon swimming event is on Sunday. Canada has two entries: Richard Weinberger of Victoria and Xavier Desharnais of Sherbooke, Que.