Messi banged in a hat-trick as Barcelona cantered to a 4-0 win over the Amsterdammers in the group stage opener at the Nou Camp, with Ajax's misery compounded in the second half when Victor Valdes saved Kolbeinn Sigthorsson's penalty.
Even though the scoreline was undeniably one-sided, De Boer saw reasons for optimism and has no fears ahead of Sunday's meeting between the perennial Dutch title rivals at the Philips Stadion.
"In the end I think the 4-0 defeat is a blow, because - again - we gave away two unnecessary goals," De Boer said of Wednesday's loss.
"Without those two goals we had almost as many chances as them.
"We certainly were not better than them, but I thought we played pretty well. I think that at times we showed good game play, despite the pressure and the lack of top form, against a big team like Barcelona.
"We have shown that we are able to play good football."
Asked about his side's chances against PSV this weekend, he replied: "I think we are favourites."
De Boer's confidence is sure to be tested by a PSV side who have had a marginally better start to the campaign than Ajax and currently sit second in the standings after three wins and three draws in their opening six games.
For their part, Ajax are two places and a point worse off after dropping points in three matches so far this season - including a 3-2 reverse at AZ Alkmaar last month.
Also on Sunday, surprise leaders PEC Zwolle will travel to Vitesse Arnhem looking to maintain their place at the head of the standings, a week on from suffering their first defeat of the campaign at the hands of De Boer's Ajax.
Fifth-placed AZ travel to NAC Breda and Feyenoord play host to FC Utrecht in Sunday's remaining games.
On Saturday bottom side NEC Nijmegen will go in search of their first win of the campaign when they travel to ADO Den Haag, Heracles Almelo welcome FC Twente, FC Groningen play host to RKC Waalwijk and Heerenveen make the trip to Roda JC.
The weekend action gets under way with a meeting between two promoted teams on Friday night, as Go Ahead Eagles play host to Cambuur Leeuwarden.