Josh Morris grabbed to matchball and launched himself into double figures for the season, with Neal Bishop capping two personal milestones with a fine effort from the edge of the area.
"Delighted! Apart from a five minute period before half time, I thought we were magnificent," he told The Iron PlayerHD.
"The performance had everything we were looking for. The commitment to the game, the energy, the decision making and the quality on show when we were on the ball was superb.
"I've been told we've got a good record here in recent years but this is a tough place to come. They beat Bolton here and were undefeated for a few games.
"They came back at us and got a goal and Luke (Daniels) made a magnificent save just after that and it would have been unjust if they had got an equaliser, but that's football.
"The goal just after half time gave us that cushion again and we played very well after that point."
Alexander spoke highly of his entire squad on the night, from the strikers who led the line to the defence which again remained resilient.
"Both goals in the second half were brilliant strikes," he continued.
"We could've scored a couple more but to score four against Walsall, we are delighted. I thought Hops (Tom Hopper) was magnificent tonight and led the line really well and Josh and Duane caused them a lot of problems.
"They both deserved their own goals on the night for the work they've done for the team."
On what was a landmark evening for midfielder Bishop, starting for the Iron for the 100th time and for the 500th time in his professional career, he capped it with a brilliant strike just after half time to re-establish the two goal lead.
"I can't speak highly enough of Bish," he stated.
"He's a great example to the younger players. That's his 500th career start in professional football, but he's played hundreds of games before that.
"He had a sore ankle from Saturday but he's put himself out there and the commitment from him is top notch. It was a great strike and it just settled the game down for us again.
"It's a great pat on the back for Bish on a landmark night."
Jordan Clarke was withdrawn at half time, with his replacement Scott Wiseman claiming an assist for Morris' hat-trick goal. The United boss reacted to the alteration.
"He fell awkwardly on his ankle just before half time," said Alexander.
"He was in a bit of pain and unfortunately couldn't carry on. Scott Wiseman came in just continued the performance and that's the importance of the squad. When players get their opportunity, they have to perform like that.
"That's the importance of training at the maximum level and being ready."