As you know you are ~2 levels higher than me ... FWIW, some points to think about ...
SHORT COMMENTARY
* You seemed to be stuck in the past and chastising yourself for prior lost points. Clear your head. Be in the moment. I believe your self-talk did you in.
* You played him as if you were playing a right-handed partner.
LONG COMMENTARY
1) If there is one aspect of your play in this match i can pinpoint your loss on it's your 'self-talk' - it got you passive and doubting yourself TOO much!! IIRC one long point in the 3rd game, you both pushed, no one attacked ... ultimately you lost the point ... easy for me to say, hard for you (
and me to do) - break out of the funk/negative self-talk you had. Relax. Stop living in the past. It's over. Move forward.
What is your best attack? Pendulum side down then 3rd ball loop? Serve that more, get your loop in, you have to work your confidence up. Early in match, your loops didn't make it consistently - but as you looped more later and they started landing in, you started looping more.
"Success breeds confidence and confidence breeds success." Sometimes though it's not about your best attack, but exploiting your partner's weakness. It seemed you didn't vary your serves early on to probe for his weaknesses... test him, probe him, serve here, serve there, serve long, serve short, serve fast, serve slow. Or perhaps you already knew his weakness. Even if that was the case, i would still vary serves, he may have an off day or something. Varying serves, if nothing else, makes it less predictable.
2) If there is one other obvious aspect of the match to my eyes, it is that your strategy wasn't flexible. It seemed like you played him as if you were playing a righty ... most of your balls/returns were to his FH ... if you played a righty, generally shots would be to your partner's BH as that is generally weaker than their FH.
Since your parnter is a lefty, your shots were to his FH ... granted some balls to his FH won for you, but it seemed like you lost more than you won ... helped him to attack you more.
Again, perhaps due to your past play with your partner, you have identified your partner's FH as his weakness which is why your strategy was to hit balls to his FH.
3) I have old man memory, recall watching you play him before, but don't recall details. Did you serve short top/sidetop to him this match? I think perhaps once you did in the first game. He popped it up on the 1st or 2nd point. Wonder if you served top/sidetop a bit more to test him on his receive on both his BH and FH, what would've happened? Wonder if this was a weakness as he popped up a 2nd ball. Or was it no spin you served?
4) Do you have a rocket serve? Would have liked to see you launch one down the line to his BH to test him.
He seemed to mix in his rocket serves with 50/50 success both to your BH and FH early on. The 4th game though, he seemed to serve 80% rockets to you (and once in a while serve a pure sidespin ... his placement is like He Zhimen's)
5) It was clear that he was going to serve a tomahawk serve when he did. Early in the match, you returned successfully. Later it seemed it got you a bit. But he stopped serving tomahawk to you as he thought his rocket serves were your weakness.
6) Didn't seem you used your RPB too much. I feel that is one of the strongest aspects of your game along with your slow and controlled spinny FH loop.
Is your partner an oldschool PH? From his grip though, it suggests a modern PH style, but he seemed NOT to have used a RPB in the entire match. Didn't seem he punched at all. Just BH block.
While on the subject of grips, I didn't notice your grip before until now. Despite playing modern PH style, your grip is closer to an oldschool PH grip to my eyes.
7) 4th game - early - one long rally, both pushing, you finally went for a RPB loop and it didn't land in. You were noticeably affected by it. May have set you off on a downward spiral. Take a slightly longer pause to clear your head before you play. Be in the moment. Again easy for me to say, hard to do sometimes.
Later, you both pushed, long pushing match, no one attacked, you won the point luckily when he netted his push. You were really shaken up and didn't seem to recover from a few points earlier and was hesitant to attack.
8) You seemed to serve 2 or 3 BH serves, and all other serves were pendulum and 75% if not more were to his FH.
I may be totally wrong in my commentary. Hope this helps!
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Props to bobpuls for cluing us in on what your partner was doing. He seemed to stop it in the 4th game.