Bednar headed home a Marek Cech cross in the 83rd minute before Beattie struck in stoppage time to earn Albion a second successive home win.
It was no more than Albion deserved as they had dominated proceedings only to be frustrated by goalkeeper Heurelho Gomes.
Tottenham had to play for 55 minutes with ten-men after Benoit Assou-Ekotto had been sent for a lunge on Gianni Zuiverloon.
But Albion were unable to make that extra manpower pay thanks to the heroics of Gomes before Bednar and Beattie finally found a way past the Brazilian.
Tottenham have now won just one of their last four games and the initial success enjoyed by Harry Redknapp when he took charge at White Hart Lane is fading into the distance.
Tottenham were fortunate to get to half-time with the only damage being the loss of Assou-Ekotto.
Albion dominated the opening skirmishes without being able to turn that pressure into goals.
James Morrison shot wide after a mazy run from Cech before Gomes came to Tottenham's rescue.
After Michael Dawson had fouled Luke Moore on the edge of the area in the 13th minute, Borja Valero whipped in a free-kick that Gomes did well to tip away.
Despite the best efforts of Darren Bent who tested Albion goalkeeper Scott Carson in the 22nd minute, Tottenham struggled to really carry a threat.
Their cause was not helped when Assou-Ekotto saw red after 35 minutes following a rash challenge on Zuiverloon.
Referee Steve Tanner had no hesitation in immediately reaching for the red card when the former Lens defender made a studs-up challenge on the Dutch Under-21 international.
Albion almost made their extra manpower pay off straight away when Jonas Olsson headed a Jonathan Greening corner goalwards only to see Gomes pick out the ball just under is bar.
Gomes continued his heroics immediately after the re-start by spectacularly tipping a Chris Brunt free-kick over the bar.
He then denied Zuiverloon as Tottenham were rocking in the face of an Albion assault.
Dawson cut out a goalbound drive from Zuiverloon before Gomes again came to Tottenham's aid by tipping a deflected 75th minute drive from Graham Dorrans over the bar.
Albion looked set to have to accept a share of the spoils before Tottenham's resistance was finally broken.
The impressive Cech lifted in a right-wing cross and Bednar escaped the attentions of Dawson to head home from eight yards.
Tottenham had to chase the game after that and Albion exploited the space they left in stoppage time.
Cech picked out Morrison and he ended his run into the area by picking out the unmarked Beattie, who made no mistake from six yards.