Ladbrokes Chief Executive Jim Mullen said the Cheltenham horse racing festival - which saw many heavily backed bets win - had "taken the shine off" off a generally favourable period.
"At Cheltenham we were reminded of the intense competition with offers and pricing at levels which, in our view, abandoned bookmaking principles," he said.
"We competed hard but refused to pursue unsustainable strategies and our stance remains that we will compete where we know we can get the right returns from the right customers."
He added that despite the blip things would stabilise throughout the year:
"We are currently a little ahead of our plans on key customer metrics and benefited from favourable results up until Cheltenham. However, experience tells us to expect results to normalise over time. We remain confident to deliver a result in line with our expectations."
Group net revenue jumped 10.6% in the three months up to March 31, while digital net revenue jumped 36.5% as online betting grew in popularity.
European retail also did well, up 6.5% (and 8.4% on a constant currency basis).
The report also said that Ladbrokes still have a liability of about £3 million should underdogs Leicester City Football Club win the Premier League, and that a key focus of the second quarter was the UEFA European Championships.
As Business Insider previously reported, 2015 was a tough year for the bookmaker. It made a £43.2 million loss, though this was mainly down to expensive restructuring rather than poor odds making.
Investors responded well the first quarter results, with shares rising sharply on Thursday morning before stabilising at £11.91:
