Fluid connector systems including first and second connector portions couplable together to form a fluid pathway therethrough, and can resist fluid flow through the connector when the connector portions are separated from each other. A connector portion can include a connector housing, a luer portion, and a deformable valve member. The deformable valve member is disposed within the connector housing and includes a spherical portion extending partially through a valve opening of the connector housing. The spherical portion defines a slit, and the deformable valve member is configured to selectively prevent fluid flow from the housing volume through the valve opening and to deform to expand the slit and permit fluid flow from the housing volume through the valve opening.