Fly-half Ryan Lamb kicked the other 14 points for Saints who, strengthened by the return of their international contingent from World Cup duty, have put a poor start to the season firmly behind them.
Victory stretched their recent run to three wins in the Aviva Premiership and two in the LV= Cup.
Wasps, denied their third successive Premiership win, replied with tries by England centre Riki Flutey and lock Ross Filipo and a penalty from fly-half Nick Robinson.
But defeat provided a miserable end to a week which saw coach Shaun Edwards and veteran England lock Simon Shaw sever their connections with the club.
England lock Courtney Lawes made his presence felt after only three minutes with a crunching, but totally fair, tackle which left Robinson needing several minutes of treatment before regaining his feet.
Ten minutes later Wasps lost former England prop Tim Payne to the sin-bin for throwing a punch after a maul ended with several players involved in a scuffle.
A minute after his departure, the home side fell behind when another messy breakdown provided Lamb's first penalty.
Despite being temporarily reduced to 14 men, Wasps responded with a try from Flutey after Lamb's second failure to find touch with a penalty enabled the home side to counter-attack.
Left-wing Tom Varndell did extremely well to put England winger Chris Ashton under pressure as he chased a through kick from scrum-half Joe Simpson and the loose ball was picked up by right-wing Christian Wade whose pass put Flutey in.
Lamb and Robinson - with a superb kick from the halfway line - exchanged penalties before Lamb was denied by an unusual use of the video replay.
Referee Tim Wigglesworth went to the television match official when the Northampton players complained after the touch judges failed to award Lamb a penalty when his 29th-minute kick sailed high above the posts.
After considering the issue for more than three minutes, the fourth official backed the touch judges by ruling out the score.
Lamb put the disappointment behind him to kick Saints into a 12-8 interval lead with two long-range penalties.
Northampton increased their lead two minutes into the second half with Tonga'uiha's try.
After the Saints forwards piled into a ruck to turn over possession, Lawes, centre Tom May and left-wing Vasily Artemyev combined to get close to the Wasps line.
The Russian winger was hauled down just short but released the ball for Tongan World Cup star Tonga'uiha to pick up and dive over.
Not to be outdone, fellow prop Mujati matched him with Northampton's second try 12 minutes later.
Taking a short pass from scrum-half Lee Dickson, Mujati crashed through a tackle by Robinson to run 30 metres unchallenged and touch down between the posts, leaving Lamb an easy conversion.
Lawes produced another bone-shaking tackle which felled home full-back Hugo Southwell before being withdrawn by Northampton director of rugby Jim Mallinder.
Wasps produced a late surge but Wade - the Premiership's leading try-scorer - was denied his seventh of the season by Artemyev as the pair contested a high kick to the corner from home scrum-half Joe Simpson.
The pressure finally paid off with a 70th minute try in the left corner for Filipo. Wasps continued to attack but were denied a losing bonus point.
Gilbert has released a new line of rugby cleats. The Gilbert Virtuo 8S is part of the exciting new product. Check it out.
The entire All Blacks apparel line has been updated for 2013/14. Check out the New Zealand All Blacks polo.
The Nike Tiempo is a solid rugby cleat and one of few styles still made from full-grain natural leather.
The Gilbert Blitz 8S rugby cleat is a great cleat at a great price of $69.99. Get a new pair of cleats today.
A cool looking all black rugby cleat with the high performance adidas is known for. Get in the Gear!
Wear the crest of the British and Irish Lions on your t-shirt. A great look for the summer.
The All Blacks Performance t-shirt is black with hints of blue from the training jersey. Very Cool.
The New Zealand All Blacks training jersey for 2013/14. Get in the Gear!
The USA Rugby Pro Alternate rugby jersey is perfect for any fan of the Eagles. Get yours to wear during the summer Test matches.
The NEW All Blacks 2013/14 jersey has arrived at World Rugby Shop. Dare to wear the colors of the All Blacks.