Preston sacked manager Graham Westley in midweek and installed John Dreyer as caretaker after the club had won just once in League One since November.
But Stuart Beavon lifted the gloom with a fine strike after 19 minutes and Bailey Wright doubled the lead before the break to end leaders Bournemouth's run of five successive wins.
"It is difficult," said Howe. "We weren't at our best there is no doubt about that, we were second best, which is really difficult for me to say because it hasn't happened yet.
"This is the first time. We were slow out of the traps, we conceded two poor goals, we never really had any concerted pressure on their goal and I think we have to try and forget this as quickly as possible.
"We have to learn from it and analyse it, which we will, but we have some massive games coming up which will define our season, so we are going to look to that and try and put this one to bed quickly.
"You can look to a combination of factors, we have had a lot of travelling, we have had a lot of games, we have some tired bodies.
"It was a really poor pitch again, it was the same for both sides and we didn't adapt to it. I'm not looking for excuses but we have to move on."