The Dutchman and his stallion Don VHP Z outpaced rising German star Maurice Tebbel on Chacco Boy and Swiss star Martin Fuchs with Chaplin to win the latest leg of the Longines Global Champions Tour.
"[Don VHP Z] is very consistent on this level," said Smolders. "When I walked the course for the first round it looked tough so that was in our advantage at the moment. And I know he loves this place -- he was second the last two years -- and with seven in the jump-off I had a good shot and with this jump-off it suited him.
"I could make the right angles and his scope made the difference today. For sure it's always possible to go faster, like Martin showed, and with Maurice at the end I knew there were very fast combinations who are young and hungry still to come so I was definitely not sure, but I thought a podium place was possible."
His win in Hamburg means Smolders, who dominated the 2017 LGCT season, qualified for the inaugural Longines Super Grand Prix in Prague at the end of the season.
"I'm very pleased that I am qualified," he said. "My horses are probably not the real winners, but they are very consistent and today was one of the few chances for me to win one [of the qualifiers] and I had that feeling and the scenario went like I wanted.
"I am very pleased with that. I only did two Globals so far, but we will for sure be there at St Tropez and Cannes and hopefully we can climb up the leaderboard."
The next leg of the LGCT takes place in St. Tropez, France from May 31 through June 2.
After five legs of the 16-leg competition, Britain's Scott Brash remains in the lead in the overall standings with 131 points after Edwina Tops-Alexander failed the qualify for the jump-off. The Australian is lying in second place with 119 points, followed by Ben Maher, also from Britain, with 103 points.
Both Brash and Tops-Alexander are trying to become the first rider to win the overall LGCT championship three times.
Global Champions League
Earlier in the day, Belgium's Pieter Devos and Under-25 rider Laura Klaphake of Germany helped St Tropez Pirates clinch their first win of the 2018 season as they triumphed in the Longines Global Champions League.
With the top four teams separated by just four penalties, or one fence, of each other, the crowd was presented with a thrilling finale to the two-day team event.
In a tough course set by Frank Rothenberger, only 17 of the 56 starters jumped clear in the second round.
"That is what this is about, putting the pressure to the end," said Devos, who produced two clear rounds with two different horses over two days. "It was a super competition, it was really important to be clear. Laura did a super round, but had one down so I knew I had to go clear. It makes extra pressure, but makes everything more exciting. That's what is is all about it was super sport today."
Holland's Jur Vrieling and Germany's Marcus Ehning pushed Valkenswaard United up two spots to finish second with just four penalties in the second round. The Shanghai Swans, with riders Pius Schwizer of Switzerland and Shane Sweetnam of Ireland, finished in third place.
"It is a really good team and a pleasure for me to be part of this team," said Tebbel of Valkenswaard United. "Today was a bit unlucky for us, but second place is really good."
It was a tough second round for Berlin Eagles, who had been in the lead after the first round but crumbled under the pressure with former Olympic champion Ludger Beerbaum of Germany making 12 faults on Chiara while team-mate Philipp Weishaupt produced eight penalties.
London Knights remain the overall leaders of the Global Champions League, improving on their 16th place after the first round to fifth after a strategic overnight change of horse and rider. Valkenswaard United are second while their Hamburg victory pushed St Tropez Pirates into third place.
The top 16 ranked teams this season will qualify for the inaugural Global Champions Play Offs in Prague in December, which has a record prize pot of $10m, including $3m for the winning team.