The most anticipated duel of the opening day was turned upside down when Olympic champion Dobrynska leapt a season's best of 6.57 meters in the long jump and overtook Ennis at the top of the standings. The British defending champion finished with 6.19 and fell back into third place.

World heptathlon champion Chernova was even more disappointing with a 6.25 to languish in fourth place just hours ahead of the concluding event.

Australian hurdler Sally Pearson lived up to her billing instead. She set a continental record of 7.85 seconds in the 60-meter hurdles heats and saw one of her toughest rivals, American hurdler Kristi Castlin, fail to finish her race since she thought everyone would be pulled back for a false start.

Many racers complained about the starting gun and tough acoustics in the Atakoy Arena.

In the shot put, outdoor world champion David Storl, Olympic champion Tomasz Majewski and Reese Hoffa all qualified directly for Friday's final.

In a packed morning program, Ethiopian great Meseret Defar set off on her quest to become the first female athlete to win five world indoor gold medals in a row, easily winning her 3,000 heat.

"My feeling is good and my shape is good," Defar said.

The opening day started exceptionally good for Ennis. She bolted out of the blocks of the 60 meters hurdles and immediately left the taller Russian with an unbridgeable gap. The Briton crossed in 7.91 seconds, and led Chernova by a big .38 seconds.

Then, Ennis extended her lead by clearing 1.87 meters in the high jump, compared to Chernova's 1.84. Then Ennis set a personal best of 14.79 meters in the shot put as Chernova fell further back.

After a good shot put came her weak long jump to open up the whole competition.

With four of five events over, Dobrynska had 4,065 points, leading Austra Skujyte of Lithuania with 3,978 and Ennis with 3,972. Chernova had 3,807 points.

"I've always said it's not just between me and Chernova, it's an Olympic year and everyone raises their game and we can see that," Ennis said.

Beyond the title on Friday, the clash is also about bragging rights going into the London Olympics. Chernova beat Ennis in the seven-event heptathlon at the world championships in Daegu, South Korea, last year, and Ennis badly wants some gold of her own going into her home games.

In the men's heptathlon, things were clear almost from the start with American world record-holder Ashton Eaton taking a big lead after two events. He set a personal best of 8.16 meters in the long jump to open up a 2,060-1,909 gap over Olerksiy Kasyanov of Ukraine after two of seven events.

In the high jump, world champion Anna Chicherova eased into the final, clearing 1.95 meters without missing a single jump.

Chaunte Howard Lowe of the United States also went over the qualifying height and was joined by Olympic champion Tia Hellebaut, who was facing elimination when she cleared 1.92 on her third and final attempt.

In the 400, Sanya Richards-Ross and Aleksandra Fedoriva won their heats to advance to Saturday's final.