Defending champions South Africa have begun this year's tournament with a victory, but they were far from convincing as they scraped a narrow 17-16 Pool D win over Wales in Wellington.
Frans Steyn and Francois Hougaard both scored tries for the Springboks, while Morne Steyn kicked two conversions and a penalty in a tight affair
Toby Faletau went over for Wales' sole try, with James Hook contributing 11 points with his kicking.
The result was tough on a gallant Wales side, who led 16-10 with 15 minutes to play before Hougaard's try between the posts gave South Africa the upper hand.
Even then, the match was not over, with Rhys Priestland and Hook missing a drop goal chance and a tough penalty respectively.
South Africa started with 11 of the 15 players who won them the trophy four years ago, but they will need to improve on this display if they are to retain their title.
There were two other pool matches played on Sunday, the third day of the tournament.
Australia, who like South Africa are attempting to win their third world title, scored 26 unanswered second half points to defeat Italy 32-6 in their Pool C opener at North Harbour.
And, also in Pool C, Ireland saw off United States 22-10 in their opening match in New Plymouth.