The Kenyans were up 5-0 until they lost a man to the sin-bin for a high tackle as Curry when to score in the corner and were awarded a penalty try.
Akira Ioane crossed soon after for a 14-5 lead but the Kenyans, who were thrashed 31-7 by Great Britain in their earlier match, continued to frustrate the world No.2 side.
Williams was ruled out for the rest of the tournament with the serious injury after he took a crash ball into two defenders early in the second half.
The woes did not end there with Joe Webber dislocating a shoulder in the defeat. Curry said they were guilty of making too many mistakes.
"Without the ball it's pretty hard to score and when we got it we knocked it on or turned it over at the ruck."
Tietjens said the team's loss against Japan was not for lack of preparation.
"We prepared, we planned. It just wasn't to be, it was just one of those games," he said.
"Japan, to their credit, played very, very well.
"We made a lot of mistakes. We tended to rush instead of being composed."
Tauranga sailor Sam Meech fared well in his day's races.
In his third of 10 races he placed fifth and in the fourth race later in the day he placed sixth.
He is currently in third standing overall behind Argentina's Julio Alsogaray in first and Croatia's Tonic Stipanovic in second.
He races again tomorrow.
Bay competitors up tomorrow:
Hockey:
The women's Blacks Sticks, featuring Tauranga players Gemma Flynn, Sam Charlton play Spain at 1am.
Rugby sevens:
Scott Curry in the men's team who will play Great Britain at 3.30am.
Sailing:
Sam Meech in the men's laser class at 4.05am and 5.30am.
Jason Saunders in the Mixed nacra 17 at 4.05am followed by race two and three later in the day.