A new move. It makes sense to develop the knight here, to escape from the move e4-e5.
1. d2d4  1... d7d5  2. c2c4  2... e7e6  3. g1f3  3... d5c4  4. e2e4  4... b7b5  5. a2a4  5... c7c6  6. b1c3 A rare move, but the game will quickly transpose to a well-known position. 6... f8b4 Now we're back to a position with more than a thousand games played. It makes sense for Black to try to exploit White's move order with the move 6...b4. Considering the time spent, it's likely Tan didn't expect this opening and was improvising from this moment on. 7. c1d2  7... d8b6 Another rare move, this time leading to truly unexplored positions already on move eight, something we also saw in the first game of the match. 8. f1e2 