The pub chain, which announced record half-year profits in March, saw like-for-like sales growth decrease by 0.8% (compared with marginal growth in the first half) in the 13 weeks to 25 April 2010.
This means year-to-date like-for-like sales are now down 0.2%, although company sales (which include the boost from new openings) are up 4%.
The company said with sales, profit and cash-flow at the business proving resilient despite recent increases in prices due to tax rises, it had now adopted a more cautious outlook in regards full-year performance.
JD Wetherspoon has opened 26 new pubs this financial year with the closure of two. It now expects 45 new sites to open during the year rather than 50 as previously forecast.