Strikes by Southern Railway workers on Thursday and Friday have been called off to allow fresh talks in the bitter row over the role of conductors.
Members of the Rail, Maritime and Transport (RMT) walked out on Monday and were due to stay out until the weekend.
Following an offer from the RMT to suspend the action if Southern returned to talks without any preconditions, Acas announced that the strike will be suspended.
A spokesman for the conciliation service said: "Southern and the RMT are returning to talks tomorrow under the auspices of Acas. Strike action has been suspended for Thursday and Friday."
RMT general secretary Mick Cash said in a message to members that he had contacted Southern with a way forward to resolve the dispute.
"Please be advised that I have now received communication from the conciliation service Acas informing me that the company will now enter into negotiations with our union officials without any preconditions.
"The National Executive Committee has had time to consider this matter and have acknowledged that some progress is being made. As the company have now agreed to meet with our union officials without the caveat of any preconditions the NEC has therefore instructed me to inform you and your colleagues that the strike action has now been suspended with immediate effect until further notice.
"You and your colleagues are therefore instructed to return to work for all shifts commencing from 22.00hrs tonight.
"I would like to congratulate you all on your steadfast and unwavering support for your colleagues during this dispute and the bravery and strength of unity you have shown during this difficult time."
A Southern spokesman said: "We are encouraged that the RMT has accepted our offer to resume talks at Acas and has agreed to call off its strike action.
"For our passengers' sake we truly hope these talks will be productive and bring this long-running dispute to an end.
"At present, the strike timetable is still in the industry train planning systems for Thursday and Friday. Regrettably, this means tomorrow's service will be based upon the present strike timetable, but we will do our very best to add services in and extend the hours of operation wherever possible.
"On Friday we plan to revert to the revised timetable operating before the strike. We will update our website www.southernrailway.com as further information becomes available."