Four spectators were arrested after the incident on Court 18.
Hanescu had won the opening two sets on tie-breaks, and had match points in the third.
But a tie-break went against him and German opponent Daniel Brands then levelled the match by taking the fourth set 6-3.
Hanescu then fell behind in the deciding set before the incident which was followed by the 28-year-old from Bucharest opting to retire from the match.
A Scotland Yard spokeswoman said four men were being questioned under the Public Order Act after the Romanian complained to officers.
The spokeswoman said: “Police were called to Court 18 following a disturbance.
“Four youths were arrested. They have all been taken to a south London station under Section 5 of the Public Order Act.”
Meanwhile, Wimbledon champion Roger Federer resumed normal service at SW19 yesterday with his first straight-sets victory of this year’s championships.
The six-times winner, who dropped three sets in the opening two rounds, eased past Frenchman Arnaud Clement 6-2 6-4 6-2.
Clement, 32, failed to push the top seed with his forehand misfiring and serve disintegrating in the final set but Federer showed all of his class on Centre Court.
The 28-year-old now faces a reunion with Austrian Jurgen Melzer, who came from behind to knock out fellow seed Feliciano Lopez 4-6 6-3 6-2 6-4.
Novak Djokovic set up an intriguing fourth-round contest against former champion Lleyton Hewitt with a convincing triumph over Albert Montanes.
The third seed had faced a difficult five-set opener against Olivier Rochus but he followed up his straight-sets win over Taylor Dent by beating the 28th-seeded Spaniard 6-1 6-4 6-4.
Djokovic was always in control but seems certain to face a difficult encounter after 2002 champion Hewitt eased to a straight-sets win over France’s Gael Monfils.
Hewitt triumphed 6-3 7-6 6-4 to cement his status as an outside title contender.
Andy Roddick won in four sets against Philipp Kohlschreiber of Germany after taking control of the contest in the third set.
Roddick broke at the final opportunity to take the first set 7-5 but the German then saved three set-points before edging a tie-break to level. However, last year’s beaten finalist stepped up a gear to take both remaining sets 6-3.
Roddick will now face Yen Hsun-Lu of Chinese Taipei, who reached the fourth round of a grand slam for the first time.
The 26-year-old won both opening sets against Florian Mayer 6-4 6-4 before the German retired with a leg injury.
Tomas Berdych, Andy Murray’s conqueror in the French Open, overcame two tie-break losses to edge past Denis Istomin of Uzbekistan.
The 12th seed, who reached the semi-finals at Roland Garros, won the final two sets 6-3 6-4 following three tie-breaks.
In the second round, John Isner’s unforgettable tournament ended in anti-climax as the jaded record-breaker suffered a 6-0 6-3 6-2 defeat to Dutchman Thiemo De Bakker. Less than 24 hours after winning the longest match in tennis history, which comprised 183 games over 11 hours and five minutes, Isner slumped out in just one hour and 14 minutes. He later pulled out of the doubles tournament with a toe injury.
De Bakker will play France’s world number 63 Paul-Henri Mathieu, who shocked 13th seed Mikhail Youzhny with a five-sets triumph.