RIO DE JANEIRO (AFP) - Belgium's Nafissatou Thiam sealed a dramatic victory over defending champion Jessica Ennis-Hill in the seventh and final event of the heptathlon on Saturday.

Thiam, 21, went into the 800m with a narrow 142-point lead over the Briton, knowing that if she finished within nine seconds of her rival gold would be hers.

The Belgian did just that, finishing at 7.47sec to amass a total of 6,810 points, 35 points ahead of Ennis-Hill, with Canada's Brianne Thiesen-Eaton claiming bronze (6,653).

"It's crazy!" said Thiam. "I wasn't expecting that - maybe top eight, but not the gold.

"It was very hard coming back from being injured. I wasn't sure if I would even make these Games. But with the physio we did a lot of work and it worked."

Thiam, who combines athletics with university studies in geography, clocked 13.56sec in the 100m hurdles, jumped a best of 1.98m in the high jump, managed 14.91m in the shot put and timed 25.10sec in the 200m during the first day of action.

That handed Ennis-Hill a 72-point overnight lead.

But on the second day, Thiam turned the screw. She went out to 6.58m in the long jump and threw a monster 53.13m in the javelin before the 800m showdown.

Her high jump, shot put and long jump were all leading marks, cancelling out her disastrous 200m, which was 25th fastest of the field.

Ennis-Hill, who became a mother last year, had been bidding to become only the third woman to retain an Olympic athletics title after giving birth. But she was left happy with silver.

"This is my last Olympics, and it's strange knowing I won't be at another major championships like these," she said. "I'm going to have a break and go on holiday and spend time with my family.

"These were my second Olympics and to win gold at my first and silver here makes me so proud. I can't wait to get home and show the medal to my son."