Gikiewicz angrily pushed one masked person back and urged others to return to the stands. The fans looked primed for violence, angered after Hertha supporters burned stolen Union jerseys, flags and scarves, while firing fireworks onto the field during and after the game.
One landed dangerously close to the Union bench, leading referee Deniz Aytekin to suspend play and lead both teams off the field, while another landed in the crowd among Union supporters, close to the children and partner of forward Sebastian Polter.
"I was shocked. Nobody wants that. Thankfully, no one was hurt," said Polter, whose 90th-minute penalty on Saturday gave Union a 1-0 win over its city rival.
Other Union players, including Keven Schlotterbeck and Christopher Lenz, supported Gikiewicz and prevented an already volatile situation from spiraling into violence.
"It's our duty to save our fans from stupidity," Polter said. "We wanted to hold the fans back before it escalated."
Union defender Christian Gentner said the players were the only ones at this point who could have prevented the angry ultras from attacking their rivals.
This iiiiiisss thee maaaainn eveeeent of the evening!!! Introducing first, fighting out of the red corner: the reigning, deeeefeeeending, undisputed Champion of the World: Rafał #Gikiewicz #unionhertha pic.twitter.com/MzNb5IRb02
— Out of context Polish football (@OfPolski) November 3, 2019
"We wanted to ensure that we could celebrate this special victory and not that it came to violence," Gentner said.
The majority of Union fans celebrated the 32-year-old Gikiewicz for his actions by chanting the goalkeeper's name.
"Perhaps he has a new job as a security officer once his career ends," joked teammate Robert Andrich.
Police said a Union fan and police officer sustained minor injuries from the fireworks, while another officer was injured while on duty. There were four arrests and 25 cases are being brought for offenses including assault and trespassing.
About 1,100 police officers were on duty for the game, with local officials supported by forces from other federal states.
The German soccer federation has initiated an investigation into the disturbances.
It was the Bundesliga's first Berlin derby involving teams from either side of the formerly divided city. Union is the first team from what was East Berlin to compete in Germany's top division since the league was restructured following German reunification.
Hertha, based in the west of the city, competed in the West German league system while Union played in the East German Oberliga.
The city celebrates 30 years since the fall of the Berlin Wall on Saturday.