Dublin's Aoife Clark was ranked overnight 12th after a formidable Olympic performance on Master Crusoe in the first day of dressage in Olympic Three Day Eventing at Greenwich Park today.
The 30 year-old, riding the Irish-bred Master Crusoe, recorded a penalty score of 48.90, which gives her a marked advantage when she begins the next phase of the event on Monday.
Germany's Dirk Schrade clocked up an impressive 39.8 penalty points.
Clark said her "heart sank" when she had to follow Schrade's commanding performance.
She said: "It's a little bit daunting going in after the current leader, my heart sank a bit when I saw his score.
"But I'm thrilled with the horse. It's our first championship so to go in there and do a good test was great.
"I loved the atmosphere. I know the horse really well and I trust him not to blow up and to really try when he goes in."
Cork's Michael Ryan was the first of the Irish team into the arena with Ballylynch Adventure, finishing on a dressage score of 60.20, while Mullingar's Joseph Murphy completed the day on 55.60 penalties with Electric Cruise.
Germany's Ingrid Klimke leads the overnight rankings with Butts Abraxas on a dressage score of 39.30.
A total of 74 horse-and-rider combinations make up the 13 nations taking part as teams and individuals in Three Day Eventing.
Sunday sees Kildare's Camilla Speirs and the petite (151cm high) Portersize Just a Jif enter the dressage arena at 11.52, with Ireland's last team member, the experienced Mark Kyle from Wicklow, perform his test with the grey Coolio at 15.10.
The second phase of the three-day event is cross-country, which takes place on Monday, followed by show jumping on Tuesday, when medals will be decided.
Ireland's eventing team at London is, in alphabetical order:
Aoife Clarke - Master Crusoe (Owner Lily White Syndicate)
Mark Kyle - Coolio (Owners Ronnie Bartlett & Mark Kyle)
Joseph Murphy - Electric Cruise (Owners Noel Good, Jill Andrews & A O'Callaghan)
Michael Ryan - Ballylynch Adventure (Owners: Carol & Tom Henry & Sheila Foley)
Camilla Speirs - Portersize Just a Jiff (Owners Bridget & Camilla Speirs)
Germany's Dirk Schrade, who clocked up an impressive 39.8 penalty points.