Bookmaker William Hill's trading performance would have been better without the remarkable success of a single tipster, the company revealed.
The news came as the bookmaker unveiled plans to return up to £300 million to shareholders, offsetting poor results from its sports betting business.
Following a first-half in which punters generally triumphed over bookmakers, William Hill said there were signs of improvement in recent weeks.
Gross win - the amount left behind by unsuccessful punters - was up 5.5 per cent in the nine weeks to August 30, compared with a 0.3 per cent in the first half.
Chief executive David Harding said that current trading would have improved had it not been for the success of the Racing Post's influential tipster, Pricewise.
"It could have been better - Pricewise, the UK's leading tipster, has had a winning tip every Saturday for the last ten weeks," said Harding.
"That 5.5 per cent could have been better if it wasn't for him," he said, adding that the winning streak came to an end on Saturday.
"A lot of people in the shops had been following Pricewise blind, so we always knew it would be a good day when he lost," he said.
William Hill became Britain's largest bookmaker in May when it scrapped plans to return £450 million to shareholders so it could buy 624 betting shops from rival Stanley Leisure for £504 million.
Investors were disappointed and since then its shares have lagged the sector by four per cent, but analysts were upbeat about the new plans to return cash.
"This time there appear to be no acquisitions on the agenda to justify changing that plan," Citigroup analysts said in a research note.
The company plans to return £ 200 million to £300 million to shareholders over the next 18 months via share buybacks.
Chief operating officer Tom Singer: "It will start in the next few days."
Profit before tax and exceptional items was £109.2 million in the first half of the year, down nine per cent on last year's first half, but in line with analyst forecasts.
William Hill's winnings from punters over the counters of its 2,100 betting shops fell by 11 per cent, while winnings from telephone bets fell 17 per cent.
But this was partly offset by a 35 per cent increase in winnings from fixed odds betting terminals (FOBT's), which allow punters to gamble on animated roulette wheels and animated horses and dogs.
The group's interactive channel increased winnings by 17 per cent, largely driven by a 151 per cent increase in poker revenues.
Profit before finance charges and exceptional items was £123.9 million pounds in the six months to June 28, compared with £132.5 million in last year's first half.
The group announced on Friday that more than 750 staff shared a £9 million windfall this month as a share scheme matured. Staff who bought shares at a discounted price three years ago have more than trebled their money
Analysts had expected a slump in profits for William Hill after Hilton Group last month reported a 6.3 per cent drop in first-half profits at its Ladbroke's gaming arm.
Ireland's Paddy Power also reported a dip in first-half profits last week, blaming poor horse racing results.