The Spanish women, making their Olympic water polo debut, let a three goal advantage slip out of their hands in the final quarter, leaving themselves under pressure to score in the last minute on Friday to secure the group win.
"We needed to score, so it was a bit tense. We kept calm and we scored," said Anni Espar, who scored the final goal with less than 10 seconds left, netting herself a hat-trick.
Australia, one of the favourites for a podium finish, handed Russia their first defeat of the tournament in a game that ended 11-8 to the Stingers.
There are eight teams in the women's water polo tournament split into two groups.
All of the teams go through to the knock-out stages but theoretically winning the group is an advantage as it means a match against a lower ranked team from the opposite group in the quarter finals, scheduled for Sunday.
"We've come here for one job and that's to get the gold medal so just six games, three down, just ticking the boxes as we keep going," Australia's Nicola Zagame, 21, said after scoring a cool four shots out of four attempts.
Britain play Italy in the evening sessions, with both sides looking to post their first win of the tournament, while the United States, another medal hope who took home silver in Beijing, take on China, in games that will decide the final group rankings.
Szilveszter Fekete believes his Great Britain side can still book their place in the Olympic semi-finals despite three straight defeats.
The hosts will now play top-ranked Spain in the quarter-finals following a 10-5 defeat to European champions Italy.
"We always play close matches with Spain, we had tight ones in the European qualifications, in the world league prelims, and the last time we met in Barcelona we lost 9-7 with Spanish referees on the poolside," said Fekete.
"To be honest we are not broken. We wanted to play a great match in front of our supporters, but losing to the European champions should not be regarded as a tragedy."
Chloe Wilcox admitted she has been surprised by some team's rough tactics but insists other nations are starting to take Great Britain seriously.
"Teams are not coming into matches feeling that they've got a guaranteed win anymore. In training, the Australians didn't want us poolside. I think they're a little bit scared of us now," she said.
"It was not our goal to finish last in the group, but on the up side it does mean we play Spain next. We only lost narrowly to them in a recent match and we can do well against them."
"But we do not want to play aggressive water polo. It is a game of skill and we are not interested in getting into a brawl."