(Adds detail)

COPENHAGEN, Oct 27 (Reuters) - Danish brewer Carlsberg posted third-quarter underlying sales that beat expectations on Tuesday and raised its full-year earnings guidance thanks to strong sales in Russia and China.

The world's third-biggest brewer, whose brands also include Kronenbourg, Baltika and Holsten, now expects 2020 operating profit, excluding the effects of any acquisitions, to decline by a mid-single-digit percentage, compared with previous guidance of a high-single-digit decline.

The upgrade was due to a strong performance in the third quarter, continued positive volume trends in Russia and China at the beginning of the fourth quarter, and the effects of planned cost reductions, Carlsberg said in a statement.

Beer sales have suffered during the COVID-19 pandemic, but as some countries, including China, Carlsberg's biggest single market by volume, relaxed lockdowns over the summer, the company has seen a rebound enough to prompt it to raise its outlook last month.

Still, as a result of new coronavirus restrictions following a recent spike in infections, sales at restaurants and bars "face an increasing level of pressure in the coming quarters", Carlsberg said.

Volumes sold at bars and restaurants fell by a fifth in the third quarter compared with last year, it said.

Carlsberg reported sales - excluding the effects of any acquisitions - between July and September of 17.3 billion Danish crowns ($2.8 billion), compared with an average forecast of 16.9 billion from analysts polled by the company.

Shares in Carlsberg have dropped around 20% from an all-time high of 1,064.5 crowns in January.

($1 = 6.2952 Danish crowns) (Reporting by Nikolaj Skydsgaard and Jacob Gronholt-Pedersen Editing by David Goodman and David Holmes)