Is it possible to play decent chess after you've had a few drinks? For me, definitely not, but there are plenty of stories of chess masters still effortlessly winning while a little worse for wear. But I think there are just as many stories of alcohol affected players that have ended badly.
Nonetheless I once had an opponent who was having such a bad weekend that he decided to sink a few over lunch before the final round commenced. While his game started erratically, he sobered up as the game wore on, and finished his tournament with a win.
While reading a copy of The Guardian Weekly on the bus this afternoon, I noticed Leonard Barden made notice of the performance of one the teams in this years Russian Teams Championship. Apparently Tomsk (the defending champions) were fined for a "sports discipline breach". In the old days this was Soviet code for heavy drinking. In his column Barden presented the following game, lost by a Tomsk player, and said "Judge for yourself"
Najer,E - Belozerov,A [C43]
Russian Teams ICCF, 2008
1.e4 e5 2.Nf3 Nf6 3.d4 Nxe4 4.Bd3 d5 5.dxe5 Nc6 6.0-0 Be7 7.Nc3 Bf5 8.Re1 0-0 9.Bd2 Nxd2 10.Bxf5 Nxf3+ 11.Qxf3 g6 (D)
12.Rad1 gxf5 13.Nxd5 Qc8 14.Qh5 Qe6 15.Rd3 Nxe5 16.Rh3 h6 17.Nxe7+ Qxe7 18.Qxh6 Nf3+ 19.gxf3 1-0