With the breeze at their backs, Waikato were behind early to a Glenn Dickson penalty before the Bath-bound Stephen Donald landed a 55m penalty of his own to level the scores.
Speight, who played for the Brumbies in this year's Super 15, gave the Mooloos the lead after stepping inside two tacklers to cross outwide.
Leonard, playing in his 50th match for Waikato, added a second midway through the half after Donald found Jackson Willison on the outside before slipping the ball to the halfback to scoot 25m to score.
Up 15-3, Waikato relaxed somewhat and former All Black prop Kees Meeuws was held up over the line before a piece of Popoalii brilliance got Otago back into the game.
The New Zealand sevens representative stepped his way past four defenders from 38m out to grab a memorable try and Dickson's conversion had the hosts leading 15-10 at the interval.
Otago started the second half brightly and centre Jayden Spence failed to get a toe to the ball with the tryline begging and then a minute later wing Matt Faddas was denied a try in the corner by another national sevens rep, Tim Mikkelson.
In a match littered with handling errors a highlight came with 10 minutes to go when a sweeping Waikato counterattack, launched from deep within their own half, was rounded off by replacement winger O'Donnell, who went over in the corner.
The home side were then recipients of a generous decision by the television match official, who awarded a try to hooker Cummings-Toone when he appeared to have dropped the ball over the line. The try gave Waikato a bonus point which could prove invaluable at the end of the season but for now put them top of the premiership table.
* Canterbury flew home with theaid of a very strong southerly windto win their match overNorthland at Christchurch.
The final result was as good as apparent at halftime when the home side changed ends just three points behind after playing into the teeth of the elements for 40 minutes.
They turned around a 10-13 deficit to register their fourth win in seven outings after Northland looked to be posing a serious threat for the first 30 minutes.
Canterbury's dominance built as the game wore on after they hit the lead for the first time nine minutes into the second half when lock Luke Romano crashed over the line after a highly organised and clinically executed rolling maul from a lineout 10m.
Penalties then followed by young first five-eighths Tyler Bleyendaal and his replacement, Tom Taylor, as Canterbury eased out to 23-13 before they ended the game with an exclamation mark when fullback Johnny McNicholl crossed for his side's bonus point fourth try after a sharp break by Taylor.
Earlier, Northland made much the better start to be 13-0 up after 21 minutes thanks to the goalkicking of wing Lachie Munro and an opportunist try to No 8 Cameron Goodhue, who latched on to a loose pass deep in Canterbury territory to dot down.
Canterbury refused to kick the ball away into the wind, keeping it in hand for as long as possible, but Northland's in-your-face defence ensured the hosts were always under pressure.
Handling errors followed, leaving Northland to apply the pressure, but Canterbury stuck to their gameplan and were rewarded in the 29th minute when a quick turnover saw the ball quickly moved to the left where pacy wing Patrick Osborne stretched his powerful legs for the duration of a 60m run to the line.
It was at this point that Canterbury discovered their accuracy, building pressure near the line with a series of pick and goes among the forwards.
The turnaround in fortunes was almost complete when bruising No 8 Nasi Manu burrowed over from one such sequence immediately before halftime.
- NZPA
