The 19-year-old, who has been gradually integrated into Alonso's side this season, made the difference at the Coliseum Alfonso Perez when he provided a clever through ball for Kylian Mbappe to score the winner late in the second half, seconds after Getafe's Allan Nyom was sent off.
The assist was Guler's fourth of the campaign for Mbappe, whose goal took him to 10 in La Liga and 50 in all competitions for club and country in 2025.
Alonso was quick to praise his young midfielder's contribution after the match. "Arda also had a good impact. We found him between the lines and he found Kylian well there," the Madrid boss said. "The goal was crucial because there was very little time left."
It was a hard-fought win for Madrid, who moved back to the top of La Liga ahead of a crucial week that includes a Champions League clash with Juventus on Wednesday and next Sunday's El Clasico against Barcelona.
The match was not without controversy. Getafe coach Jose Bordalas accused Vinicius Junior of mocking him on the touchline after substitute Allan Nyom was sent off just 39 seconds after coming on for a rash challenge on the Brazilian winger.
"Vinicius came up to me and said, ‘What a good substitution,'" Bordalas told Movistar. "I told him to get back on the pitch. Then Bellingham also said something, but it's not that important. I just don't think Vinicius should provoke."
Alonso, who had started Vinicius on the bench in favour of Rodrygo and introduced the Brazilian shortly after halftime, defended his player's competitive spirit. "Vinicius can be just as important coming off the bench as he could be starting," he said. "Coming to Getafe isn't easy, you have to roll up your sleeves. It might not be pretty, but we did what we had to do."
Madrid finished the match against nine men after Getafe's Alex Sancris was also dismissed in the 84th minute for a second yellow card on Vinicius, sealing a gritty victory that underlined their title credentials and showcased Guler's growing importance in Alonso's side.
Hansi Flick has urged Barcelona to maintain their momentum as they travel to Sevilla to face Real Betis today aiming for a fifth straight La Liga win, and the German has used the build-up to highlight the growing influence of Eric Garcia.
Joan Laporta has reignited the tension between Barcelona and Real Madrid after declaring that Los Blancos "represent power", while insisting Barcelona stand for "freedom".
Real Madrid's hard-fought victory over Athletic Bilbao came with another unwelcome injury scare, but the Spanish champions remain hopeful that Eduardo Camavinga will still feature against Celta Vigo on Sunday.
Raphinha has firmly closed the door on any exit from FC Barcelona for the foreseeable future after putting pen to paper on a new deal that keeps him at the club until June 2028.
