MacLennan showed Saturday that she's ready for a turn in the spotlight.
She delivered a knockout performance at the North Greenwich Arena to win Canada's first gold medal of the London Games. MacLennan had 57.305 points to finish ahead of Chinese favourites Huang Shanshan and He Wenna.
MacLennan was confident before the event but didn't imagine herself standing on top of the podium.
"I really just focused on, 'OK, how can I do the best routine possible?', she said. "Wherever that gets me — if I'm able to do that, then that's when I'm the happiest."
MacLennan, who followed Cockburn in the eight-woman final, looked strong and graceful throughout her routine. She was rewarded with a score that really put the pressure on the final three competitors.
"That's a really good place for me because you really have nothing to lose," she said. "You may as well just give 'er."
MacLennan was thrilled after her performance and sat down with coach Dave Ross to see what her score would be. Her eyes bulged out when she realized she had a shot at gold.
"I was shocked. It's the biggest score that I've ever gotten," MacLennan said. "I knew it would be a tough one to catch. But you never want to get ahead of yourself. You want to wait until all the competitors are done."
Cockburn, her friend and training partner, congratulated her and they sat down together to see if their scores would be high enough.
"She said, 'You're going to win. That's going to take it,'" MacLennan said. "Then we just hoped that hers would be strong enough to hold on too. She hugged me and was so proud. She's an amazing athlete and an amazing support."
It was a nerve-wracking and emotional 10-minute wait.
When Tatsiana Piatrenia of Belarus came up short, MacLennan wiped a tear from her eye, knowing she was guaranteed her first Olympic medal.
Huang was next and she bumped Cockburn down to third. He was the final competitor and was on track to challenge for gold until she dropped to her knees after losing control at the end of her routine.
Her result was a shade better than Cockburn's score — knocking the Canadian from the podium — but it gave MacLennan the gold.
"It's definitely bittersweet," MacLennan said. "Our dream was to both be on the podium no matter which way it was."
MacLennan, 23, won silver at the world championships last year and took gold at the 2011 Pan Am Games. She's also a three-time national champion.
But this was her coming-out party.
She was beaming as the gold was placed around her neck at the medal ceremony as the pockets of Canadian fans in attendance waved flags and snapped pictures before "O Canada" was played.
Cockburn was pleased for her teammate but crushed that she missed out on a medal by such a slim margin.
"Obviously I wanted to end on better than fourth," she said. "But four Olympics — I'm happy with my overall career, I'm just not happy today."
Cockburn thought her Olympic career was over after the Beijing Games in 2008, when she won a second straight silver after taking bronze in 2000 at Sydney.
She decided to give it one more go for London. Instead it was her teammate who won that elusive Olympic gold.
"We pushed each other hard in training every day," Cockburn said. "She helped me a lot as much as I helped her. I don't know what to say. She won that medal on her own of course so I'm just really proud and happy for her."
MacLennan, who stands five foot two, has rock-hard legs anchoring her 120-pound frame. The baby-faced gymnast from King City, Ont., is as polite and friendly as they come.
Ross said MacLennan is the type of athlete who would make a point to personally thank him after training sessions. He added she never got the attention that Cockburn received because the veteran was always just a little bit better.
"Some time in the last year they became equal and now maybe in the last few months, Rosie's a bit better," Ross said. "But they're so close. One day one can be better, one day the other one can be better.
"That's sort of why Rosie's been flying under the radar, because Karen is so good."
MacLennan finished seventh in her Olympic debut in Beijing four years ago. Since then, she has been working hard to keep up with the powerful Chinese duo.
"We've been pushing and pushing as hard as we can to try and match their skill and capabilities," MacLennan said. "I guess it's finally paid off a little bit."
The crowd gasped when He blew her landing. It was an unusual error from the defending champion.
"I was very surprised because China's so strong and they barely ever falter," MacLennan said. "So when that happened — it's shocking."
MacLennan suffered a concussion in May while training and had to be very careful as she prepared for London. She was in form at the most recent World Cup in Switzerland and finished ahead of second-place Cockburn.
The victory changed her mindset and boosted her confidence.
"I won that and I think that's when I started believing that maybe it was possible," she said.
She entered the Games ranked fifth in the world, two positions lower than Cockburn.
"Even though it's at the Olympics, it's still a trampoline competition," MacLennan said. "It's still the sport you love. So if you focus on that and focus on what you're doing, your training and not giving yourself any excuses leading into the Games, you can hopefully come out on top."
MacLennan was whisked around the city for interviews and news conferences after her win and planned to indulge in a little chocolate when things calmed down.
With her gold medal hanging over her red-and-white Canada tracksuit, MacLennan was proud of the fact she came up with her best performance when it mattered most.
"The only thing that would make it better is if Karen was up there standing with me on the podium," she said.