But the 21-year-old from Westmount, Que., took that as a good sign as she lost 6-4, 6-2 Wednesday in what she called "the biggest match I've played in awhile against the toughest opponent by far since my comeback from injury.
"It was my toughest test, I did OK," Bouchard said of the contest lasting just under 90 minutes on the showcase Rod Laver Arena.
The Canadian has been making a 2016 comeback following a concussion she suffered in a fall in the locker room at the US Open last year. She leaves the Grand Slam in Melbourne with wins in seven of her 10 matches so far this season after playing in China and Tasmania.
Bouchard blamed nerves and big-match stress for her elevated heartbeat during a contest in which she finished with 25 winners and 37 unforced errors, breaking only once from seven chances.
"I noticed the heart rate was up highest it's ever been in a match. I felt OK, but I was feeling how hard it was physically. Aga doesn't give you any points for free so I had to work for every one," she said after the match.
"I don't have any concussion symptoms, if so I would not be able to play. So far so good — that's the most important thing. I've been able to play three week in a row over here. That's a victory for me no matter what the my results are."
Bouchard began well, securing a 4-2 first-set lead with a break of serve on a winning drop shot. But the Canadian was unable to consolidate as her opponent broke back a game later from a double-fault.
Bouchard was broken for a second time as Radwanska claimed a 5-4 margin and secured the opener after 48 minutes on a fifth set point, an inside-out forehand winner which Bouchard could not reach.
After losing serve to start the second set, the Canadian's level dropped as Radwanska began to take control, earning a second break of serve for a 5-2 lead.
Bouchard made a last stand, earning three break points in the eighth game — all saved. Radwanska got her victory chance from a Bouchard backhand to the net before a concluding error.
Earlier Wednesday, both Toronto's Daniel Nestor and Vasek Pospisil of Vancouver made it through to the second round of men's doubles.
Nestor and partner Radek Stepanek of the Czech Republic needed just 58 minutes to dispatch Tsung-Hua Yang and Cheng-Peng Hsieh of Taiwan 6-1, 7-5 in their match, rattling off five aces and winning 86 per cent of their first-serve points.
Earlier this month, Nestor became the first player in ATP Tour history to record 1,000 doubles victories with a win in the opening round at the Apia International in Sydney.
In their match, ninth-ranked Pospisil and partner Jack Sock of the U.S. defeated Philipp Petzschner of Germany and Alexander Peya of Austria, 1-6, 7-6 (5), 7-6 (5).
In women's doubles, Gaby Dabrowski of Ottawa and Polish partner Alicja Rosolska lost their first-round match in one hour 36 minutes, falling 6-1, 7-6 to Johanna Konta and Heather Watson.
Dabrowski and Rosolska double faulted 11 times and had 31 unforced errors to 19 from Konta and Watson.
No. 13 seed Milos Raonic of Thornhill, Ont., will face unseeded Spaniard Tommy Robredo late Wednesday in second-round play. Raonic won his opener in three sets over Lucas Pouille of France.
Also on HuffPost