The Bombers conceded three goals in the opening eight minutes of the game, but recovered to claw within 15 points in the third quarter.
The visitors had plenty of chances in front of goal in the last term, but managed just 1.4.
The final scoreboard flattered the Power, who kicked away with late goals to Daniel Motlop and Justin Westhoff.
Knights said poor skills and lack of scoreboard pressure had cost his side a genuine shot at winning the game.
“We felt as if we stayed with Port long enough, we were a real opportunity to win the game,” Knights said.
“What was disappointing was when we had those opportunities to get shots on goal or score we didn’t take them and put enough scoreboard pressure on Port. We never did that.
“We could never get to that under 10-point margin, which would then put the pressure back on Port. Port was still able to play with the same freedom. They didn’t tighten up at all and we couldn’t get close enough.”
Knights lamented his side’s ball movement from defence, but said he was pleased with the performance of first-round draft-pick Michael Hurley.
Hurley, 18, looked poised in the back half and kept his direct opponent Warren Tredrea goalless.
“Michael Hurley, being a first gamer, I thought he did an outstanding job especially considering he had a gallbladder operation five or six weeks ago,” Knights said.
“Tayte Pears is a 19-year-old that hasn’t played a lot of footy and I thought he was quite competitive down back. They were two really shining lights.
“I also thought Heath Hocking did a reasonable job on Shaun Burgoyne for the day.”
Another Bomber debutant, former Crow Hayden Skipworth, also appeared comfortable at AFL level. He finished with 30 possessions and a goal.
Outsiders in Victoria have questioned Essendon’s decision to select the mature-age ball magnet and Knights said he hadn’t been proved right just yet.
“Skipworth’s vindication will come on the whole season. It will be every game,” he said.
“This weekend there were eight winners and eight losers. Some players have played very good footy and some haven’t had good weekends. When I have a look at the game, I’ll decide whether his performance today was a pass mark or if he struggled.”
Knights said he was bemused by the attention Skipworth had received since arriving at Windy Hill.
“Hayden’s just turned 26, so if he gets it right he could have five or six years- half a decade- of footy left.
“It’s interesting because around the league, clubs year after year give opportunities to veteran players and it just goes under the radar. But for some reason, people are very interested in Hayden Skipworth and, to be brutally honest, I don’t know what it is.”
