The Chiefs won their first match at home in Hamilton in over a year when they beat the Rebels by 38 points to 10.
The victory was their first win of the season and they also secured a bonus point for scoring four tries.
The Rebels were disappointing and it looks like it could be a long season for Super Rugby's newcomers. Last week their defence was sound but this week they lacked the same intensity.
Neither side looked a major force in this year's tournament as they produced error-ridden performances in a match played in constant rain.
The Chiefs eventually exploited advantages of possession and territory to post their first home win in the Super 15, though with those advantages they should have won by more.
The Chiefs created a great many opportunities, but needed 79 minutes to secure a bonus point with Masaga's second try as they wasted scoring chances with poor handling or misjudged options.
They gained the upper hand in set pieces, dominating scrums and putting pressure on Melbourne at lineouts, but they didn't fully exploit those advantages until deep into the second half.
Veteran Tana Umaga at inside center steadied a Chiefs backline that too often sacrificed concerted effort for individual opportunism.
Sivivatu was a constant attacking threat, even when he ran the ball from deep defense, and Masaga was a slick finisher when given even the sniff of an overlap.
Liam Messam, who finished the match as Waikato's captain in place of All Blacks fullback Mils Muliaina who left with a back injury, said his team had showed it had learned from early losses to the Brumbies and Highlanders.
Donald had a mixed game, kicking poorly for position and giving little direction to a backline which should have flourished with a steady supply of possession from set and loose play.
However, his reliable goalkicking-he landed seven of nine attempts-was crucial as Waikato kept its nose in front throughout the match.
Donald landed three penalties and the conversion of Sivivatu's try as the Chiefs took a 16-3 lead into halftime and he continued to slot goals from often difficult angles as the home side built on that sound advantage.
Sivivatu's 34th-minute try gave the Chiefs a buffer at halftime and Masaga built on that with his first try in the eighth minute of the second half.
Former Welsh interntional Gareth Delve scored Melbourne's only try in the 57th minute, but Waikato became steadily more dominant as the game continued.
Masaga and replacement Taumalolo scored tries in the last quarter, which expanded the advantage and snatched a four-try bonus point.
The Rebels were heavily penalized throughout the match and suffered for the lack of a sound set-piece foundation.
Final Score Chiefs 38 Rebels 10
Tries - S Sivivatu, L Masaga 2, S. Taumalolo
Pen - S Donald 3
Con - S Donald 3
Tries - G Delve
Pen - D Cipriani
Con - D Cipriani
Referee: Vinny Munro
Assistant Ref 1:Garratt Williamson
Assistant Ref 2:Shane McDermott
TMO :Ben Skeen
Chiefs : 1. Ben May,2. Aled de Malmanche,3. Nathan White,4. Craig Clarke,5. Isaac Ross,6. Scott Waldrom,7. Tanerau Latimer,8. Liam Messam,9. Brendon Leonard,10. Stephen Donald,11. Sitiveni Sivivatu,12. Tana Umaga,13. Dwayne Sweeney,14. Lelia Masaga,15. Mils Muliaina (Captain)
Reserves:,16. Sona Taumalolo,17. Hika Elliot,18. Romana Graham,19. Steven Setephano,20. Taniela Moa,21. Mike Delany,22. Tim Nanai-Williams
Rebels 1. Nic Henderson, 2. Ged Robinson, 3. Greg Somerville, 4. Adam Byrnes, 5. Alister Campbell, 6. Jarrod Saffy, 7. Michael Lipman, 8. Gareth Delve (vc), 9. Nick Phipps, 10. Danny Cipriani, 11. Cooper Vuna, 12. Julian Huxley, 13. Stirling Mortlock (c), 14. Lachlan Mitchell, 15. Mark Gerrard
Reserves: 16. Heath Tessmann, 17. Laurie Weeks, 18. AN Other, 19. Tom Chamberlain, 20. Richard Kingi, 21. Afusipa Taumoepeau, 22. Peter Betham