After a victory in Round 6, Wesley So was held to a draw by D. Harika in the next round. It was one of those rook and pawn endings where So had an outside passed pawn, but trading pawns will result in a draw. Just when So looked poised to take a commanding lead in the group, he suffered his first loss to Gm Frank Holzke of Germany in round 8. It was even for most of the game, but So committed an inaccuracy coming into the endgame. He ended up having two connected passed pawns against a bishop. These pawns, without the help of their king, would not make it to promotion because they were not advanced enough. The bishop will have no problem mopping them up.
But in Round 9, probably quite irritated by his loss, So defeated Bitalzadeh who opened with the English. Things started coming apart for White in the position you see below:
Here, 16...e6 put white between a rock and a hard place. White's only options are f4 or e3. Both will mean cutting off the bishop's escape route. Bitalzadeh played 17. Re1 which delays the inevitable for a moment. Play continued 17...Kf7 18. Nf4 h6 19. Ne6 Re8 ( better than 19...hg5 ) 20. Nd8+ Rd8 21. Bd8 Qd8 and black went on to win in 36 moves. Final position is below after 36...gh5:
The black knight can go c6 and d4. White can't double up with the rooks on the E file because the bishop controls the e1 square.