McClaren, unveiled as Nigel Clough's successor on Tuesday morning, watched from the stands later that night as Academy manager Wassall took charge of the first team in a 4-4 draw with the Tractor Boys.
Zak Whitbread had reduced the deficit to just one with a goal on his debut after arriving on loan from Leicester on Monday.
Murphy then made it 4-1 with his second goal of the night and Derby trudged off for half-time looking dead and buried.
McClaren is not due to officially begin his role until Wednesday but he took it upon himself to go down to the dressing room and deliver a rallying call to the Rams players.
And it worked as captain for the night Craig Bryson gave Derby hope early in the second half and Jamie Ward pulled another goal back on the hour.
Bryson then completed the comeback with the equaliser in the 88th minute to send Pride Park wild.
"We weren't good enough in the first half and Steve came down at half-time and had a few words to say," said Wassall.
"He made a few changes as well and it did the trick, the second half was much, much better.
"The response from the players in the second half was absolutely magnificent and that bodes well for the future.
"Steve came back down to the dressing room again at the end of the game and he was absolutely thrilled with the response."
Asked whether was McClaren angry when he addressed the players at half-time, Wassall replied: "We were all angry, the players were angry with themselves."