Championship side Watford appeared to sense an opportunity to upset their Premier league rivals and started in lively fashion.
Ross Jenkins had a diving header that dropped wide of the post and Lionel Ainsworth also lobbed debutant Lastuvka, who backtracked to tip over.
But the visitors eased themselves into the game and Boa Morte's effort from the edge of the area was heading for the top corner before Loach saved.
David Di Michele's reverse pass then sent Noble through on the Watford goal but Loach parried to deny the Hammers midfielder.
Lastuvka was the busier keeper as Watford more than held their own before being rewarded with Mullins' own goal.
West Ham manager Gianfranco Zola:
"I can't tell him (Lastuvka) anything because he made a fantastic save before he was very unlucky..
"I said to the players that it doesn't have to change our positive attitude to the work we're doing. It would be too easy to think everything would be bright
"I didn't even know about this (the tribunal ruling). I don't want to have any excuses like that."
Bookmark with:
What are these?