By Alan Baldwin

RIO DE JANEIRO (Reuters) - Claressa Shields had awarded herself a "C" after her first fight in Rio on Wednesday but it was "A" for achievement on Friday after the U.S. boxer punched through to a second successive Olympic middleweight final.

Shields, now one fight away from becoming a double Olympic champion, blasted past Kazakhstan's Dariga Shakimova in convincing fashion, forcing a standing eight count at the finish.

"I give it A minus," said the 21-year-old fighter from Flint, Michigan. "I did great. I went out there, showed my skill, showed my class. I showed I was the better, stronger and more skilled fighter.

"I actually could have stopped her, but I was having so much fun out there I was like, why do that?

"I wanted her to throw her punches at me so I could show her I'm faster than you, I punch harder than you. It was a great match."

Shields, who could become the first U.S. boxer to win two golds since 1904, is the second member of the current team to reach a final with bantamweight Shakur Stevenson going for his gold on Saturday.

The thought of that was enough for Shields to turn all musical.

"Just the two of us," she sang, getting into the swing of a familiar tune.

"We can make it if we try, just the two of us. Just the two of us. Me and Shakur. Building gold medals in the sky, just the two of us."

Shields, who will face Nouchka Fontijn of the Netherlands in the gold medal bout, will certainly be the favorite to repeat her London 2012 exploits and she is hungry on more than one level.

"I was questioning myself about my first fight, and why I was so tired," she said. "When I thought about it, the day before my last fight I didn't eat, I didn't drink the right way. I was starving my body.

"I just can't stand the food at the canteen any more at the Olympic village," she said. "I'm not going to walk all the way over just to find I'm not going to eat anything and go back to my room.

"The day before the (last) fight I drank some chocolate milk and that was it. So yesterday I made sure I ate two or three whole meals, and a lot of water."

(Editing by Nina Chestney)