He told BBC Three Counties Radio: "I thought in the first half we were very slack. We didn't respond so we had some words at half-time.
"We showed a bit of desire in the second half. They've got the message."
Striker Danny Graham hit a brace for Watford before fellow frontman Marvin Sordell drew the visitors level with less than 10 minutes to go.
This season is highly likely to be one of struggle, where success in my eyes would be survival and continued solvency
One_Lars_Melvang
Graham, 24, received special praise from his boss after playing the whole game despite suffering from a nose injury.
"Obviously he had a nasty knock and he took the ball to the face today, which is not very nice when you've got a nose problem," said Mackay.
"I have to say I thought he was fantastic today. He ran into the channels so many times, he caused them no end of discomfort and thoroughly deserved to score."
Meanwhile the club's under-15s have arrived in Northern Ireland to play in the Milk Cup tournament with 23 other sides.
Source: BBC Sport
Source: BBC Sport