I just played an ASR league game against an apparent 2D and lost only by 25 points *yay*. Could you please point out where my main mistakes were?

I was White.

A few thoughts:

Move 100: This was an interesting plan, but white has enough outside strength that you may at least consider E18 to hold black to one eye in the corner and go for an outright kill. I have not read this in depth to confirm if it works or not.

Move 108: At this point I think black is ahead by 10 or 15 points in solid territory, but white has much more potential on the board. This move tries to make territory from thickness directly, and may be better as a standard high approach at E4. If black plays the standard attachment underneath, you can try the avalanche to aim for a huge left side. Otherwise, white has enough center strength to create a decent bottom side while limiting black on the left.

I'm not certain what white should have done in the lower right, but when black is able to rescue the J11 stones and reduce the area in between white's lower left corner and the center almost completely, things have gone awry, and I think that's the ponnuki on the outside that black got.

Some comments.

White is ahead and has the move. Why ask for trouble? A high approach to the bottom left corner looks good.

Jowa says, Don't run. Better to counter-pincer. (Yes, you got lucky when Black did not attack well.)

:w108: Interesting idea.

:w110: Better to keima to E-04, and thank Black for increasing your advantage.

:b119: The last big point. White has given back much of his advantage.

:w124: What's to be afraid of? Hane.

:w128: What's to be afraid of? You are strong here. Better N-05 or R-03.

:b129: A double peep. In Black's sphere of influence. White is still ahead, but the game is close. Time to plan.

Can White give up the stone in the bottom right corner. Yes, if White gets compensation. That might come from the bottom side. O-04, N-04, N-05 are all worth considering, so that if Black cuts off the corner stone, White can continue in the bottom side.

Another possibility is to attach at R-03 in the corner and see if I can live or at least threaten to do so. One possibility is R-03, R-02, Q-04, to take care of one cut, at least for the moment. Another is S-02 instead of Q-04.

With 8 minutes left, it would be worth taking 5 minutes to think about all this.

:w130: Makes one connection, but with no guarantee of life. 11 seconds. Really?

:w132: You know the cut is coming. How about O-04. Then if Black pushes through, hane. If Black extends on the bottom side, then you can make a hanging connection.

:w138: Very important. You want, as a rule, to keep your opponent's stones separated and yours connected. You can almost play the wedge at P-03 without thinking.

_________________
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At some point, doesn't thinking have to go on?
— Winona Adkins

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Everything with love. Stay safe.

Through move 80, you captured a large B group and have a won game. Congratulations on very fine play up to that point. And even later, you played well, finally losing in a complicated fight in the lower right. Nice game.

W move 82 (R5) is a reasonable invasion/reduction. It is pretty deep into B influence, but since you have three ways to run (R3, R8, P5) you should not get into too much trouble. However, given your lead, you could have won more safely by leaving that area alone. B cannot really resist a W cut at M9 or a center expansion move like M7, so his right side moyo is not as impressive as it may appear.

W move 86 (Q8) is asking for trouble. Why not just attach at Q7 to make shape and settle your stones quickly and safely? You do not need a big reduction of B territory around here in order to win the game. In fact, you pretty much only need to avoid dying in the entire lower right quadrant. Still, you got an acceptable result through move 96.

W could play move 100 at E18 to try to capture the entire corner. The W wall to the right is infinitely strong, so B has absolutely no counter-play in that direction. It looks to me like W could actually kill everything. Even if B lives, an all out attack is not especially risky for W, as whatever territory W loses right next to the wall will be made up along the left side as B struggles to live. After B lives in the corner, without giving W much compensation, he is back in the game.

W move 108 is interesting and could be effective, but the natural follow-up is E4 if B fails to extend in that direction. Simpler alternatives would be C6 to take maximum left side territory or E3 to dispute the bottom side. The exchange through move 118 looks a little better for B, since he negates much potential W territory, while W needs one more move to completely secure the corner. After W move 122, B could still cause lots of trouble at D3.

B finally won the game by outplaying W in the fight starting with move 129, which ended up capturing the entire lower right corner. Before blocking at move 132, it would be good timing for W to switch to R3 to start making eyes in the corner (planning to answer R2 at S2). There is no need to save the O7 stones. Even at move 142, W could still play S2 and live in the corner. Missing this tesuji was probably the game losing move. Move 144 at P2 would still be a good try and might allow some of the W stones to live. The corner fight is all about liberties, so the throw-in at move 152 was bad. When W finally played P2, it was too late.