Isidor missed a golden chance moments earlier, side-footing against the post with the goal gaping, before making no mistake soon after to hand Sunderland their first points and first home win of the season. Fulham remain without a point after two matches.
Arbeloa did not hide his frustration afterwards.
"We didn't even fight, we didn't run, poor technical level. We were not in the game. We started the second half better for 10 or 15 minutes but a game is 90 minutes and we deserved to lose today," he said.
"Against Chelsea at home, it's too easy to run and fight but you have to do it every game. We are going to have some bad days with the ball but I didn't like the attitude of my team.
"It's about the character, the mentality, and ambition. We didn't win any second balls. Today I think we were not at our level."
The Fulham boss pointed to the pre-season and the Chelsea game as evidence his side can do better.
"We have been working so hard during pre-season and the game against Chelsea, I saw the attitude I want to see in my team. It has to be away too," he said.
"We have a week to prepare for the game with Palace at home. We have to fight for every ball and we need to run from the first minute to the final whistle. We have to realise we are Fulham and we have to fight."
On the transfer window, Arbeloa added: "We can do with the squad being a little bit stronger in some areas. We have two days and we are working on it."
Regis Le Bris was simply relieved to see his side back to winning ways after an opening-day defeat at Ipswich.
"It's good to be back at home and win again. The Premier League is really demanding and we faced a really good team. The lads did really well to manage their threat and create opportunities up the other side," he said.
On Isidor's near-miss and eventual winner, Le Bris added: "The first one was about being really clinical. I think the movement was really good. The second one was really good. In this league you cannot miss two in a row."
Le Bris also praised Nordi Mukiele.
"He is a really good player. He can play in two positions and he is so important for the squad," he said, before reflecting on the club's slow start mirroring last season's pattern.
"We had the exact same start last season with one win at home and one defeat. It's a new season, so a new chapter to write."
On squad business before Tuesday's deadline, he said: "The main point is that we kept the core of the squad. I'm really pleased with that. If we can reinforce the squad, then we will."