Orient scored two stunning goals in the first half, Lee Cook hammering a left-footed drive over 'keeper Karl Darlow before Dean Cox blasted home a second with an amazing shot from the halfway line.
Will Grigg scored his first goal of the season from the spot in the 58th minute after Gary Sawyer tripped Ben Purkiss, sparking a fierce Walsall fightback which saw skipper Andy Butler hit a post and a low drive by Andy Taylor well saved by Ryan Allsop.
But the O's held out, and Slade said: "We won deservedly so on reflection of the 90 minutes. In the first half I thought we were excellent, and the only disappointing thing about the first half was that we were only two up because we had good chances to make it three or four."
Asked about Walsall's late appeals for a second penalty, Slade said: "I thought we could have had a penalty in the second half when we had a player brought down. I think it would have been a travesty if we hadn't won the game.
"Fair play to Walsall, they put us under a lot of pressure in the second half but there were not too many saves my goalkeeper had to make. Walsall's keeper made two great saves in the first half."