Why did White give up his bishop at move 21? Well, if instead 21.Bd4 Qa5 22.Bxg7 Kxg7 23.Bc4 Qxa2. Now White threatens mate on a1, but if the d2-rook moves (24.Re2) ...Qxa1 snaps up the h1-rook. The rook cannot be defended either: 24.Rdd1 Qxc2#. So White doesn't have time to retreat the bishop e.g. 23.a4 Kxf7. Since the bishop is a goner anyhow, he sells his life as dearly as possible.

Dont you mean black threatens to mate on a1 but anyway bishop trade must be made now or later as 21.Bd4 Qa5 22.Bxg7(if 22.g4 hxg4 23.fxg4 Bxd4 24.gxf5 Be3 25.fxg6+ Kg7 26.h5 Qxd2+ 27.Kb1 Kh6 and game is hopeless for white)

Beginning in the next diagram, BL will have a number of opportunities to attain perpetual check, by which he could claim 3-Time Repetition draws.

After 26.Rde2 BL has the option to take a perpetual check by 26...Qa1+ 27.Kd2 Qd4+ 28.Ke1 Qg1+ 29.Kd2 Qd4+ 30.Kc1 Qa1+ etc. This perpetual is available after BL's 27th & 28th game moves also. After 29.R2e1 BL has the following perpetual check option: 29...Qa1+ Kd2 30.Qd4+ Kc1 30.Qa1+ etc. It remains available after move 30 as well. After 31.Rf2 BK has an interesting perpetual option by:31...Qa1+ 32.Kd2 Qd4+ 33.Ke2 Qe4+ 34.Kf1 Qh1+ 35.Ke2 Qe4+ etc. After 31.Rf2 has been played, BL must use care not to permit the Rooks to double upon the pinned Bf5 or the B will be lost; or worse must trade it and the Q for the Rooks which would be a loss.

It's also worth bearing in mind that, although unlikely to come about, if White could trade off all his pawns and both rooks for just Black's Q the game would be drawn (provided White's lone king retained touch with the a1-square). So if Black wants to win, he must keep his Q.

Nice game! For the end I have to say that I really can't see black winning, had white played the prosaic 35.Rxf5+. That's time trouble I guess... //Now looking the position after 35.Rxf5+ Kxh4 I think white is winning after Rfg5. The black king is very awkwardly placed in the h-file and white can make simultaneous threats for mate, queen and the black a-pawn. Black can never trade his queen for both white rooks since white would win easily the resulting pawn ending. Moreover, black can't perpetual check white since the white king is perfectly safe when he reaches b1. After checks have ended, moving a rook to position where both rooks threaten backrankers(e.g. Rg8) wins

A very interesting game. Including the final position. Make a slight change here and put the Bc2 instead at Ba2, with the move still belonging to WT and WT would Draw easily! His plan would be simply to check the BK King every move with a Rook. By doing so, he would get a draw when the position repeated for the third time; unless BL stopped that by trading his Queen for the 2 Rooks when they would check on a sq covered by the Q, such as g7 or h4. But then it is still a draw no matter where that trade is made, as long as WT leaves his pawn on b3 to be taken by the B, and just walks his K to a1 [WT MUST avoid one pitfall, which is that he must NOT play his pawn to b4 to be taken or else then BL would play axb4, making his pawn a Knight-pawn which CAN promote, instead of a Rook-pawn that CANNOT promote]. Once the WT K reached Ka1 or any contact with that square, then BL cannot win because his B is not the same color as the promotion square a1. Consequently the B and King can never force the WT K from guarding a1. [IF in that situation the B was on black squares, it could make the pawn promote on a1.] Since BL has the Bc2 in reality, it stops the Rooks from ever checking at g6. That stops his chance for perpetual rook checks to bring the 3 Time Repetition needed for that draw.

Perhaps White resigned in disgust at his last move. Instead he had a comfortable draw the previous move by 35.Rg5+ (or 35.Rxf5+) 35...Kxh4 36.Rfxf5 after which Black cannot save his a-pawn, and ought to take the draw at once. *** Can White save the final position? 36.Rg5+ Kxh4? 37.R1g4+ Qxg4 38.Rxg4+ Kxg4 39.Kd2 Bxc3 40.Kc3 a4 41.Kb2 ((=) as pointed out by ccmcacollister). So to retain winning chances Black's K must retreat: 36.Rg5+ Kh6 37.R1g4 and White may hope his play on the g-file is enough to balance Black's control over the rest of the board.

There was little mistake on move 34...Kh5 but I have now made correction to that.