Try the following script (run from groovyTestStep):
def groovyUtils = new com.eviware.soapui.support.GroovyUtils( context );
def testCase = testRunner.testCase;
def testStep = testCase.getTestStepAt(0);
//def testStep = testCase.getTestStepByName("Delay");
//def testStep = testCase.testSteps["Delay"];
testRunner = new com.eviware.soapui.impl.wsdl.testcase.WsdlTestCaseRunner(testCase, null);
testStepContext = new com.eviware.soapui.impl.wsdl.testcase.WsdlTestRunContext(testStep);
testStep.run(testRunner, testStepContext);
You can, of course, change the testStep = getTestStepAt(0) for one of the options that were placed as a comment.