Former winners William Fox-Pitt and Oliver Townend both made strong starts to the Land Rover Burghley Horse Trials in Lincolnshire on Thursday.
While dressage specialist Ruth Edge took an overnight lead on Rogersdale, Fox-Pitt and Townend are well-placed ahead of their second rides on Friday.
Fox-Pitt, who is bidding for his seventh Burghley crown, lies third aboard Seacookie, while 2009 Burghley champion Townend is fifth on ODT Sonas Rovatio, with less than three penalty points separating the top five riders.
Fox-Pitt, a member of Great Britain's Olympic silver medal-winning eventing team in London four weeks ago, will be on last year's Burghley winner Parklane Hawk in the dressage arena on Friday.
And as well as chasing Burghley's £50,000 top prize, the 43-year-old is also favourite for the FEI HSBC Classics Series, which rewards eventing's most successful rider over a 12-month period and carries a £90,000 winner's purse.
Fox-Pitt leads that event by six points from New Zealander Andrew Nicholson, with Burghley the last of this year's competitions.
"Seacookie has not had a big competition for a while and he was in a very good frame of mind," Fox-Pitt said.
"He made a couple of mistakes, but I was delighted with how he coped overall. There weren't any hairy moments."
Attention after the two-day dressage phase will switch to Saturday's cross-country course designed by Captain Mark Phillips, and Fox-Pitt added: "It's a fantastic course. It is very big and wide.
"This is not going to be a dressage competition. The cross-country ground is superb and the course looks superb."