After Adam Lallana's first goal, the hosts took a 2-1 lead thanks to goals from Goncalo Guedes (his first for Wolves) and Ruben Neves (a penalty).
Before Semedo was sent off and Gross won it to keep Brighton's European hopes alive and put an end to the hosts' obstinate defence, Kaoru Mitoma had pulled even.
The selection of Lopetegui earlier on Saturday prevented the limbo that was on the verge of engulfing Molineux and endangering their chances of surviving.
The former Spain manager will not join before Wolves' World Cup break because he is awaiting his work visa, but he will have seen enough effort to be encouraged and enough mistakes to correct.
The Seagulls are in sixth place, just three points behind the top four, while Wolves are still in the relegation zone and two points from safety despite their hard effort.
The guests got off to a strong start as Lallana picked up Lewis Dunk's probing pass to set up Solly March. The midfielder created space, but Nathan Collins deflected his goal-bound shot behind.
Wolves only enjoyed a brief respite because Lallana scored the game's first goal 61 seconds later.
Leandro Trossard received the ball from Mitoma after a promising start, and his delicate pass fell for Lallana to score a curler from 12 yards.
However, if Brighton thought Wolves would capitulate, they were mistaken, as the hosts responded in just two minutes.
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Guedes was racing to the right when Boubacar Traore noticed him, so he rode Mitoma's challenge to stay on his feet and get past Robert Sanchez.
Trossard almost added to the agitation as he lifted over from Mitoma's pass, but Molineux remained quiet.
Although Brighton was the more skilled team and was feeling good after their 4-1 thrashing of Chelsea, the atmosphere changed after 30 minutes when Dunk handled a cross from Daniel Podence.
Even though the defender's arm was raised, it still took referee Graham Scott and VAR official John Brooks five minutes to give the penalty.
Neves blasted a high pass past Sanchez with his trademark finesse; it was the first time since May that Wolves had scored twice in a league game.
It was not shocking that they lost the lead before halftime because they had only taken the lead five times this season and only kept it to win twice.
After 44 minutes, Mitoma, who had been electrifying, equalized the score by rising above Semedo to head home a cross from Lallana's far post.
Semedo had a terrible time playing against the international from Japan, but things would get worse in stoppage time.
Semedo hauled down Mitoma just outside the box as they raced down the left to reach Dunk's deep pass. Mitoma arrived first. The defender's miserable afternoon was summed up by his clumsy challenge, and he was duly ejected.
After the break, the hosts continued on a self-destructive path when March capitalized on Jose Sa's terrible pass, but the goalkeeper turned his shot wide. It was reckless and further put Wolves in distress.
After Sanchez tipped Guedes' looping header over and Sa stopped Alexis Mac Allister's free-kick after 66 minutes, Adam Webster twice nodded wide.
Even though substitute Adama Traore put Sanchez to the test, Wolves' defense was broken when Gross scored the winning goal with seven minutes remaining.
Once more, Mitoma was engaged, and when Deniz Undav touched on his cross, Gross turned to shoot from 10 yards away.
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