"It was a tough day but I feel we made some small steps forward in performance," said Williams.
"We competed better against series leaders, South Africa, than we did two weeks ago," referring to the opening pool defeat to the Blitzbokke. South Africa raced out to a 19-0 lead at halftime and even though Wales's defence improved in the second spell, their rivals scored one more converted try through Chris Dry to record a 26-0 victory.
Wales took the game to defending tournament champions England in their second pool game and were level 7-7 at halftime thanks to a Sam Cross try and Rhys Evans conversion.
The scores were still level five minutes into the second half but two late tries by England, including one by Dan Norton which took him to 150 career touchdowns, proved Wales' downfall.
"The England game was disappointing as we were level until two minutes to go and a slight lack of experience cost us some points which proved the difference in the end," confirmed Williams. "But overall, there were positive steps in some individuals performances as well as some team structures we have been working on."
Wales were determined to finish the pool stage off with a win and with four unanswered tries in the first half, Wales swept aside Portugal 45-19.
James Davies (2), Will Price and Dylan Morgans raced over with Rhys Jones adding three conversions in a dominant half. Portugal responded in the second spell with three tries but Rhodri Davies, Rhys Shellard and Iolo Evans all scored to put the game out of Portugal's reach.
"The response for the final game against Portugal was superb," said Williams. "Rhys Jones's kicking ability was to the fore, which the boys took full advantage of in scoring seven tries. It was a superb way to sign off the day and the target will be to repeat those levels of execution in our first game versus Tonga tomorrow."