The 30-year-old clawed her way back after a poor showing in the second event of the competition, the high jump. She was in 19th at that point, moving up to 10th place after a personal best of 14.81 metres in the shot put.
After running a personal best 23.32 seconds in the 200-metre event, she goes into tomorrow with 3,903 points, behind Britain's Jessica Ennis and Lithuania's Austra Skujyte in the overall standings.
"The hurdles were incredible, I was in a great place," said Zelinka. "In the high jump I was searching for that place. I put a lot of pressure on myself in the high jump, overthinking it. But that's only one of seven events, I came back strong in the 200-metres."
Brianne Thiesen of Humboldt, Saskatchewan stands 15th overall with 3,763 points. She finished her 200-metre race with a time of 24.35 seconds.
"Other than the 200-metres, I was happy with day one," said Thiesen, the fiancée of decathlon gold medal contender Ashton Eaton of the U.S. "It's my first Olympics and I'm learning a lot. I'm going to regroup now for day two."
The heptathlon concludes tomorrow with the long jump, javelin throw and the 800-metre race.
Britain's Ennis closed out the first day of the Olympic heptathlon by running the 200-metres in a personal best of 22.83 seconds to take a 184-point lead with three events left.
Ennis opened the Olympic track meet Friday morning by running the 100-metre hurdles in a heptathlon record 12.54 seconds.
"I'm absolutely elated with today, to have performed like that with two personal bests and to end it with a PB was a brilliant start to the [heptathlon]," Ennis said.
Dibaba defends title, wins 3rd gold medal
Tirunesh Dibaba, of Ethiopia, pulled away with 600 metres to go and won the 10,000-metre race at the London Games on Friday to defend her Olympic title.
Dibaba, who clinched the first women's long-distance Olympic double in Beijing four years ago by winning the 5,000 and 10,000, collected the first track gold of the London Games in 30 minutes 20.75 seconds.
Kenyans won silver and bronze, with Sally Kipyego finishing second in 30:26.37 and world champion Vivian Cheruiyot placing third in 30:30.44.