Guys let's be real; she's not going to let him win. If she does, that'll basically mean that she accepts his confession and they start to go out. And unless the author is going to follow the footsteps of Lovely Complex and Ore Monogatari, that will mean "The End" for the story.
Odds are Tanaka will lose to Yaotome. He'll either take the loss in stride, hoping that he'll win the next game, or he'll become depressed over the loss, thinking he can never win (even with a handicap) and therefore will never feel worthy enough to confess to Yaotome. Yaotome on her part will have an internal debate with herself over if she wants Tanaka to confess to her while also trying to lift Tanaka's spirits (depending on how Tanaka will take the loss). There might even be "drama" over whether or not the possible loss will result in Tanaka wanting to quit the Shogi club.
Who knows it's all speculation at this point. Let's just wait until the next chapter to see where it goes from here.