A mouse slip...

1. d4 Nf6 2. c4 e6 3. Nc3 Bb4 4. Qb3 {Botvinnik played it when he wanted to win and Bronstein played when depressed.} c5 5. dxc5 {Fighting for center.} Nc6 6. Nf3 Bxc5 7. Bg5 {Key move. White wants to keep Black's King flank tied, and prepare Queen Rook to enter the game. White has center and Black has better development. If Black finds way against white center, his better Pawns and development will prevail. As always with Botvinnik, it is matter of a tiny edge.} h6 8. Bh4 O-O 9. e3 Be7 10. Be2 b6 11. O-O Bb7 12. Qc2 Rc8 13. Rad1 a6 14. Bxf6 {In order to keep iniiative and center, White must surrender Bishops pair} Bxf6 15. Ne4 {! Now Black must return pair of Bishops or he is reduce on 3rd line.} d5 16. Nxf6 Qxf6 17. Qb3 dxc4 18. Qb5 {18. Qxb6 gives equal game.} axb5