Eugenio Chacarra produced a superb display of front-running to win the DS Automobiles 83° Open d'Italia for back-to-back titles on the DP World Tour.
The Spaniard backed up his KLM Open win in the Netherlands earlier this month with another National Open at Circolo Golf Torino.
Matt Wallace made a valiant attempt to overhaul Chacarra's two-stroke 54-hole lead but Chacarra's 64 ensured a winning margin of five at 24 under par.
He said: "I'm feeling great, winning's always fun but that's what we work for. I'm very proud of myself.
"It was a good fight, two world-class players - probably two of the best players in the world. That's what I've been dreaming of since I was little, to play against those kind of players down the stretch and I'm very proud of how I played and how I managed myself today."
Victory also earned him a place in next month's 154th Open Championship at Royal Birkdale and he added: "I'm very excited. I've never played there, I've always dreamed of playing it and been watching on TV since I was little. Excited to be out there, now it's time to celebrate and then we can focus on that."
Chacarra started with a birdie but Wallace made immediate inroads by chipping in for an eagle to halve the overnight deficit.
Niemann also birdied that hole but suffered a double-bogey six at the next. He and Wallace birdied the fourth, Wallace with a long putt across the green, before Chacarra responded with a perfect tee-shot at the par-three next to retake the lead with a birdie.
The Spaniard repeated the dose on the eighth for the first of three birdies in a row around the turn, with a pinpoint approach to the ninth and an 11-foot putt at the next.
Wallace bogeyed the sixth but rebounded immediately with a birdie, as he has after four of his five dropped shots this week, and kept himself in touch with another gain at the ninth as Chacarra threatened to pull away.
Joakim Lagergren's surge up the leaderboard set the clubhouse target at 17 under, the Swede making nine birdies including three in a row from the 13th in a 63.
Chacarra remained five clear of that mark, and three ahead of Wallace, despite his birdie attempt at the 13th hanging stubbornly on the lip of the hole.
Wallace birdied the next to cut the margin to two but Chacarra, whose own birdie putt horseshoed out, virtually closed out the title at the following par five with a superb eagle putt from 35 feet.
Wallace gamely made his birdie to stay within three but came up inches short of another at the 16th and bogeyed the 17th, leaving Chacarra with a four-stroke cushion.
He serenely parred the last and said: "I think it's been 20 rounds in a row under par. I'm doing an incredible job with my caddy and staying patient and enjoying golf.
"Like I said, I proved myself already. When I was an amateur, I was one of the best, in America (in college), I was one of the best, and I want to be one of the best players in professional golf so that's what we're working for.”
Chacarra is only the fifth player to win the Dutch and Italian Opens in the same year and the first since Ramón Sota - the uncle of Seve Ballesteros - in 1971, with the other three instances all in the 1950s.
Wallace, who finished with a bogey for a 67 and second place on his own, had the consolation of the US$40,000 Nexo Course Record Award for his 62 on Friday.
Edoardo Molinari had set the record at 63 the previous day and Wallace joked that he may have jeopardised his Ryder Cup chances by taking the record away from the beloved Vice Captain on his home course.
He said during an on-course interview on Sunday: “If I do keep (the record) - I asked my manager this morning if I could do this - Edoardo had a great round on the first day, and it’s his home course, so I’ll donate a little bit towards him and the golf club, maybe for the juniors here, if we do keep it.”
Niemann pipped Lagergren to third with a birdie at the last, with Angel Ayora completing the top five at 16 under to win the Franco Chimenti Memorial Award.
The prize - established by the Italian Golf Federation and the Franco Chimenti Foundation in honour of the former FIG President who played a key role in bringing the Ryder Cup to Rome in 2023 - is awarded to players born in 2001 or later who have yet to win and are not ranked in the top 15 of the order of merit on any of the major Tours.
Jeff Winther, Richie Ramsay, Oliver Lindell and Daniel Rodrigues were a shot behind Ayora on 15 under.
