Cameron Norrie returned to action after pulling out of the Korea Open and Japan Open due to illnessCameron Norrie returned to action with victory over Russia's Aslan Karatsev in the last 16 of the Stockholm Open.
Britain's number one pulled out of the Korea Open last month through illness and had to come from a set down before winning 6-7 (8-10) 6-3 6-4.
The 27-year-old is battling to qualify for the season-ending ATP Finals.
Dan Evans, Norrie's Davis Cup team-mate, beat France's Constant Lestienne 6-2 6-1 to reach the last eight of the European Open in Antwerp.
Norrie committed to playing five tournaments in six weeks in a "big push" to break into the world's top seven to qualify for the ATP Finals, which take place in Turin, Italy, in November.
But those plans were derailed when the world number 12 pulled out of the Korea Open less than an hour before his quarter-final against the United States' Jenson Brooksby.
Norrie said he was suffering from jetlag after beating Japan's Kaichi Uchida 6-2 6-2 in the previous round.
He was unable to recover in time to play in the following week's Japan Open and, after moving on to the European indoor season, was pushed all the way on his return against Karatsev.
Norrie was twice broken by the world number 45 when serving for the opening set, at 5-4 and 6-5, before eventually losing it on a tie-break.
He had to battle back from a break down to win the second set and did so again in the decider, coming from 4-2 behind with successive breaks before serving the match out to love.
Dan Evans also beat Constant Lestienne in the San Diego Open quarter-finals in SeptemberEvans, 32, had no such trouble at the European Open, taking just an hour and 15 minutes to see off world number 69 Lestienne, converting five of six break points in a clinical display.
The British number two faces a possible quarter-final against Canada's number two seed Felix Auger-Aliassime, who is due to play France's Manuel Guinard in the last 16 on Thursday.
Briton Jack Draper, who has risen to number 48 in the world, plays number one seed Hubert Hurkacz in the second round later on Wednesday, while Britain's women's number two Harriet Dart is in action against Spain's Cristina Bucșa in Rouen, France.
