In front of just 2,425 fans, McDiarmid Park's lowest weekend crowd of the season, the Perth side completed a hat-trick of victories this term over Kilmarnock.
The Ayrshire side rarely showed any threat going forward and their hopes of snatching a share of the spoils relied on Saints frittering away chances.
Davidson scored a 58th-minute opener and the home fans finally relaxed when substitute Tade rose to double their advantage five minutes from the end.
Saints manager Steve Lomas had to tweak the line-up which lost to Hearts in midweek, with Chris Millar drafted in for suspended Paddy Cregg and Steven Anderson replacing injured centre-back Fraser Wright, while Nigel Hasselbaink stepped in for Newcastle loan player Mehdi Abeid.
For Killie, Kenny Shiels brought in Ryan O'Leary for Rory McKeown but gave the rest of the side which lost out to Hibs in the Scottish Cup an opportunity to redeem themselves.
Saints forged a shooting chance in their first attack with a Murray Davidson cutback picking out Rowan Vine. The striker got his shot away but it clipped Hasselbaink to slip wide of the target.
In the ninth minute home keeper Alan Mannus dealt easily with a raking 25-yarder from William Gros. It proved to be a rare first-half foray from the visitors.
Perth striker Steven MacLean tried to release Hasselbaink but keeper Cammy Bell was alive to the threat posed by the Dutchman, diving at his feet to mop up the danger.
Vine carved out a chance in the 19th minute after a Liam Craig lay-off but his shot was scooped over the Killie crossbar.
And in the 22nd minute the former QPR striker was presented with a golden chance to secure the lead when a Dave Mackay cross from the right eluded a posse of players, only to lean back and thrash a 12-yard shot high into an empty stand.
Another MacLean pass teed-up Millar but once again the ball ended up among the plastic seats rather than in the net.
In the 32nd minute Millar's delicate chip saw MacLean evade the Killie offside trap to sprint through for a head to head with the keeper - but Bell closed down the angle and got a vital touch which saw the ball bobble slowly past the far post for a fruitless corner.
Within two minutes of the restart Killie midfielder Sammy Clingan's crisp 25-yard shot ripped wide of the post.
Saints finally made the breakthrough in the 58th minute when the Kilmarnock defence failed to deal with a Craig corner kick to the back post and the loose ball was rammed home from seven yards by vice-captain Davidson.
Killie almost levelled within seconds when a teasing Gros cross clipped Anderson and spun past the post with Mannus helpless.
Killie skipper Jamie Fowler was cautioned for handball in the 65th minute before Garry Hay replaced Jeroen Tesselaar and ex-Saint Cillian Sheridan took over from Jude Winchester.
In the 68th minute MacLean again found himself one-on-one with Bell from a Craig pass and again the keeper blocked his shot.
Saints pitched in Tade for Vine in the 69th minute and Kris Boyd came on for Gros in the 77th minute, with Abeid on for Hasselbaink in the 81st minute.
With five minutes remaining Saints wrapped up three precious points when the unmarked Tade rose to power home a Craig cross from eight yards.
On-loan Swansea winger Gwion Edwards got a brief run from the bench for MacLean as Saints ran down the clock.
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